Waveguide device, and antenna device including the waveguide device

ABSTRACT

A waveguide device includes an electrical conductor including an electrically conductive surface, a waveguide extending alongside the electrically conductive surface, and an artificial magnetic conductor extending on both sides of the waveguide. The waveguide includes a first portion extending in one direction, and at least two branches extending from one end of the first portion, the at least two branches including a second portion and a third portion that extend in mutually different directions. A waveguide defined by the electrically conductive surface, the waveguide surface, and the artificial magnetic conductor includes an enlarged gap portion at which a gap between the electrically conductive surface and the waveguide surface is locally enlarged.

This is a continuation of PCT Application No. PCT/JP2018/017976, filedon May 9, 2018, and priority under 35 U.S.C. § 119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2017-094677, filed May11, 2017, the entire contents of which are incorporated herein byreference.

1. FIELD OF THE INVENTION

The present disclosure relates to a waveguide device, and an antennadevice including the waveguide device.

2. BACKGROUND

Examples of waveguiding structures including an artificial magneticconductor are disclosed in the specification of U.S. Pat. No. 8,779,995,the specification of U.S. Pat. No. 8,803,638, the specification ofEuropean Patent and H. Kirino and K. Ogawa, “A 76 GHz Multi-LayeredPhased Array Antenna using a Non-Metal Contact Metamaterial Waveguide”,IEEE Transaction on Antenna and Propagation, Vol. 60, No. 2, pp.840-853, February, 2012, A. Uz. Zaman and P.-S. Kildal, “Ku Band LinearSlot-Array in Ridge Gapwaveguide Technology, EUCAP 2013, 7th European,A. Uz. Zaman and P.-S. Kildal, “Slot Antenna in Ridge Gap WaveguideTechnology,” 6th European Conference on Antennas and Propagation,Prague, March, 2012. An artificial magnetic conductor is a structurewhich artificially realizes the properties of a perfect magneticconductor (PMC), which does not exist in nature. One property of aperfect magnetic conductor is that “a magnetic field on its surface haszero tangential component”. This property is the opposite of theproperty of a perfect electric conductor (PEC), i.e., “an electric fieldon its surface has zero tangential component”. Although no perfectmagnetic conductor exists in nature, it can be embodied by an artificialstructure, e.g., an array of a plurality of electrically conductiverods. An artificial magnetic conductor functions as a perfect magneticconductor in a specific frequency band which is defined by itsstructure. An artificial magnetic conductor restrains or prevents anelectromagnetic wave of any frequency that is contained in the specificfrequency band (propagation-restricted band) from propagating along thesurface of the artificial magnetic conductor. For this reason, thesurface of an artificial magnetic conductor may be referred to as a highimpedance surface.

In the waveguide devices disclosed in the specification of U.S. Pat. No.8,779,995, the specification of U.S. Pat. No. 8,803,638, thespecification of European Patent and H. Kirino and K. Ogawa, “A 76 GHzMulti-Layered Phased Array Antenna using a Non-Metal ContactMetamaterial Wavegude”, IEEE Transaction on Antenna and Propagation,Vol. 60, No. 2, pp. 840-853, February, 2012, A. Uz. Zaman and P.-S.Kildal, “Ku Band Linear Slot-Array in Ridge Gapwaveguide Technology,EUCAP 2013, 7th European, A. Uz. Zaman and P.-S. Kildal, “Slot Antennain Ridge Gap Waveguide Technology,” 6th European Conference on Antennasand Propagation, Prague, March, 2012, an artificial magnetic conductoris realized by a plurality of electrically conductive rods which arearrayed along row and column directions. Such rods are projections whichmay also be referred to as posts or pins. Each of these waveguidedevices includes, as a whole, a pair of opposing electrically conductiveplates. One conductive plate has a ridge protruding toward the otherconductive plate, and stretches of an artificial magnetic conductorextending on both sides of the ridge. An upper face (i.e., itselectrically conductive face) of the ridge opposes, via a gap, aconductive surface of the other conductive plate. An electromagneticwave of a wavelength which is contained in the propagation-restrictedband of the artificial magnetic conductor propagates along the ridge, inthe space (gap) between this conductive surface and the upper face ofthe ridge.

SUMMARY

In a waveguide such as an antenna feeding network, branching portionsmay be provided on a waveguide. At a branching portion, the directionthat the waveguide extends branches out into two or more. At such abranching portion, an impedance mismatch will occur unless somecountermeasure is taken, thus resulting in unwanted reflection of anelectromagnetic wave to propagate. Such reflection not only causespropagation losses of signals, but may also cause unwanted noises.

An example embodiment of the present disclosure provides a waveguidedevice in which a degree of impedance matching at any branching portionof a waveguide is enhanced.

A waveguide device according to one example embodiment of the presentapplication includes an electrical conductor including an electricallyconductive surface, a waveguide including an electrically-conductivewaveguide surface opposed to the electrically conductive surface, andextending alongside the electrically conductive surface, and anartificial magnetic conductor extending on two sides of the waveguide.The waveguide includes a first portion extending in one direction, andat least two branches extending from one end of the first portion, theat least two branches including a second portion and a third portionthat extend in mutually different directions. A waveguide which isdefined by the electrically conductive surface, the waveguide surface,and the artificial magnetic conductor includes an enlarged gap portionat which a gap between the electrically conductive surface and thewaveguide surface is locally enlarged. The size of the gap between theelectrically conductive surface and the waveguide surface is greater atthe enlarged gap portion than at any site on the waveguide that isadjacent to the enlarged gap portion, and is smaller than a distancebetween the electrically conductive surface and a root of the waveguide.At least a portion of a junction at which the first portion becomesjointed with the at least two branches of the waveguide overlaps the gapenlargement, as seen through in a direction perpendicular to theelectrically conductive surface.

According to an example embodiment of the present disclosure, in atleast a portion of a branching portion of a waveguide, a gap between awaveguide surface, and an electrically conductive surface is enlarged.As a result, the degree of impedance matching at the branching portionof the waveguide is enhanced.

The above and other elements, features, steps, characteristics andadvantages of the present disclosure will become more apparent from thefollowing detailed description of the example embodiments with referenceto the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing a non-limitingexample embodiment of a waveguide device according to the presentdisclosure.

FIG. 2A is a diagram schematically showing an example embodiment of thepresent disclosure for a waveguide device 100, in a cross sectionparallel to the XZ plane.

FIG. 2B is a diagram schematically showing another example embodiment ofthe present disclosure for the waveguide device 100 in FIG. 1, in across section parallel to the XZ plane.

FIG. 3 is another perspective view schematically showing theconstruction of an example embodiment of the present disclosure of thewaveguide device 100, illustrated so that the spacing between aconductive member 110 and a conductive member 120 is exaggerated forease of understanding.

FIG. 4 is a diagram showing an exemplary range of dimension of eachmember in the structure shown in FIG. 2A.

FIG. 5A is a diagram schematically showing an electromagnetic wave thatpropagates in a narrow space, i.e., a gap between a waveguide surface122 a of a waveguide member 122 and a conductive surface 110 a of theconductive member 110 according to an example embodiment of the presentdisclosure.

FIG. 5B is a diagram schematically showing a cross section of a hollowwaveguide 130 according to an example embodiment of the presentdisclosure.

FIG. 5C is a cross-sectional view showing an example embodiment of thepresent disclosure in which two waveguide members 122 are provided onthe conductive member 120.

FIG. 5D is a diagram schematically showing a cross section of awaveguide device according to an example embodiment of the presentdisclosure in which two hollow waveguides 130 are placed side-by-side.

FIG. 6A is a diagram schematically showing an example embodiment of animpedance conversion structure (impedance transformer) which is used ina microstrip line.

FIG. 6B is a diagram schematically showing an example embodiment of amicrostrip line construction in which a notch is provided for widthadjustment at a branching portion.

FIG. 7 is a perspective views schematically showing a portion of thestructure of a waveguide device according to a comparative example ofthe present disclosure.

FIG. 8A is a perspective views schematically showing part of thestructure of a waveguide device according to a comparative example ofthe present disclosure.

FIG. 8B is a diagram showing enlarged the structure near a branchingportion 136 in FIG. 8A.

FIG. 9A is a perspective view schematically showing part of theconstruction of a waveguide device according to an example embodimentstructured so that the distance between the waveguide surface 122 a ofthe waveguide member 122 and the conductive surface 110 a of theconductive member 110 is decreased at impedance transformers.

FIG. 9B is a diagram showing enlarged the construction near a branchingportion 136 in FIG. 9A.

FIG. 10 is a diagram schematically showing a cross-sectional structureof the waveguide device in FIG. 9A as taken along a plane which passesthrough the first portion 122A of the waveguide member 122 and isparallel to the YZ plane.

FIG. 11 is a diagram showing an equivalent circuit of the waveguidestructure in FIG. 9A.

FIG. 12A is a perspective view schematically showing a portion of thestructure of a waveguide device according to Example Embodiment 1 of thepresent disclosure.

FIG. 12B is an upper plan view showing the waveguide device of FIG. 12Aas viewed from the +Z direction.

FIG. 12C is a diagram showing the waveguide device of FIG. 12A as viewedfrom the +Y direction.

FIG. 12D is a view exclusively showing the waveguide member 122, out ofthe waveguide device of FIG. 12B.

FIG. 12E is a diagram showing a variant of the waveguide device shown inFIG. 12D.

FIG. 13 is a diagram showing an equivalent circuit of the ridgewaveguide according to Example Embodiment 1.

FIG. 14A is a diagram showing an example embodiment of a waveguidedevice having a staircase-shaped impedance matching structure, as in thecomparative example shown in FIG. 9A.

FIG. 14B is a diagram showing an example embodiment of a waveguidedevice having an impedance matching structure such that the width of thewaveguide surface 122 a increases toward the branching portion 136, asin the comparative example shown in FIG. 8A.

FIG. 15A is a diagram showing still another variant of ExampleEmbodiment 1.

FIG. 15B is a diagram showing still another variant of ExampleEmbodiment 1.

FIG. 16A is a diagram showing still another variant of ExampleEmbodiment 1.

FIG. 16B is a diagram showing still another variant of ExampleEmbodiment 1.

FIG. 17A shows frequency dependence of the input reflection coefficientin the construction of the comparative example shown in FIG. 9A.

FIG. 17B shows frequency dependence of the input reflection coefficientin the example embodiment illustrated in FIG. 14A.

FIG. 18A is a perspective view schematically showing part of thestructure of a waveguide device according to Example Embodiment 2 of thepresent disclosure.

FIG. 18B is an upper plan view showing the waveguide device of FIG. 18Aas viewed along the Z direction.

FIG. 19 is a perspective view schematically showing part of thestructure of a waveguide device according to Example Embodiment 3 of thepresent disclosure.

FIG. 20A is a perspective view schematically showing a portion of thestructure of a waveguide device according to a variant of ExampleEmbodiment 1.

FIG. 20B is an upper plan view showing the waveguide device of FIG. 20Aas viewed from the +Z direction.

FIG. 21A is a perspective view schematically showing a portion of thestructure of a waveguide device according to another variant of ExampleEmbodiment 1.

FIG. 21B is an upper plan view showing the waveguide device of FIG. 21Aas viewed from the +Z direction

FIG. 22A is a perspective view schematically showing part of thestructure of a waveguide device according to Example Embodiment 4 of thepresent disclosure.

FIG. 22B is an upper plan view showing the waveguide device of FIG. 22Aas viewed from the +Z direction.

FIG. 23A is an upper plan view showing enlarged only the waveguidemember 122 in the structure shown in FIG. 22A.

FIG. 23B is an upper plan view showing a variant of Example Embodiment4.

FIG. 24 is an upper plan view showing a waveguide device which includesa waveguide member 122 having three branches as viewed from the +Zdirection, as another variant of Example Embodiment 4.

FIG. 25A is a perspective view showing part of the structure of awaveguide device according to still another variant of ExampleEmbodiment 4.

FIG. 25B is an upper plan view showing the structure of FIG. 25A asviewed from the +Z direction.

FIG. 26A is a perspective view showing a portion of the structure of awaveguide device according to Example Embodiment 5 of the presentdisclosure.

FIG. 26B is an upper plan view showing the structure of FIG. 26A asviewed from the +Z direction.

FIG. 27 is a perspective view showing enlarged only a portion of thewaveguide member 122 for ease of understanding

FIG. 28 is a diagram showing an equivalent circuit of a ridge waveguideaccording to Example Embodiment 5.

FIG. 29A is a cross-sectional view schematically showing another exampleembodiment of the impedance transformer.

FIG. 29B is a cross-sectional view schematically showing still anotherexample embodiment of the impedance transformer.

FIG. 30A is a diagram showing an example embodiment where, as viewed ina direction perpendicular to the conductive surface 110 a, the dimensionof a gap enlargement 141 along the width direction of the first portion122A of the waveguide member decreases toward the first portion 122A.

FIG. 30B is a diagram showing an example embodiment where, as viewed ina direction perpendicular to the conductive surface 110 a, the dimensionof a gap enlargement 141 along the width direction of the first portion122A of the waveguide member increases toward the first portion 122A.

FIG. 30C is a diagram showing an example embodiment where a gapenlargement 141 of an elliptic shape is provided in a central portion ofa branching portion of the waveguide member, without reaching the edgeof any of the first portion 122A, the second portion 122B, or the thirdportion 122C.

FIG. 30D is a diagram showing an example embodiment where a gapenlargement 141 of a semicircular shape is located adjacent to an end ofthe first portion 122A of the waveguide member

FIG. 31A is a diagram showing still another variant of a waveguidedevice according to an example embodiment of the present disclosure.

FIG. 31B is a diagram showing still another variant of a waveguidedevice according to an example embodiment of the present disclosure.

FIG. 32A is an upper plan view of an array antenna according to anexample embodiment of the present disclosure as viewed from the +Zdirection.

FIG. 32B is a cross-sectional view taken along line B-B in FIG. 32A.

FIG. 33A is a diagram showing a planar layout of a waveguide member 122Uof a first waveguide device 100 a according to an example embodiment ofthe present disclosure.

FIG. 33B is a diagram showing a planar layout of a waveguide member 122Lof a second waveguide device 100 b according to an example embodiment ofthe present disclosure.

FIG. 34A is a cross-sectional view showing an example embodiment of thepresent disclosure where only a waveguide surface 122 a, defining anupper surface of the waveguide member 122, is electrically conductive,while any portion of the waveguide member 122 other than the waveguidesurface 122 a is not electrically conductive.

FIG. 34B is a diagram showing an example embodiment of the presentdisclosure in which the waveguide member 122 is not on the conductivemember 120.

FIG. 34C is a diagram showing an example embodiment where the conductivemember 120, the waveguide member 122, and each of the plurality ofconductive rods 124 are composed of a dielectric surface that is coatedwith an electrically conductive material such as a metal.

FIG. 34D is a diagram showing an example embodiment of the presentdisclosure in which dielectric layers 110 c and 120 c are respectivelyprovided on the outermost surfaces of conductive members 110 and 120, awaveguide member 122, and conductive rods 124.

FIG. 34E is a diagram showing another example embodiment of the presentdisclosure in which dielectric layers 110 c and 120 c are respectivelyprovided on the outermost surfaces of conductive members 110 and 120, awaveguide member 122, and conductive rods 124.

FIG. 34F is a diagram showing an example embodiment of the presentdisclosure where the height of the waveguide member 122 is lower thanthe height of the conductive rods 124 and a portion of a conductivesurface 110 a of the conductive member 110 that opposes the waveguidesurface 122 a protrudes toward the waveguide member 122.

FIG. 34G is a diagram showing an example embodiment of the presentdisclosure where, further in the structure of FIG. 34F, portions of theconductive surface 110 a that oppose the conductive rods 124 protrudetoward the conductive rods 124.

FIG. 35A is a diagram showing an example embodiment of the presentdisclosure where a conductive surface 110 a of the conductive member 110is shaped as a curved surface.

FIG. 35B is a diagram showing an example embodiment of the presentdisclosure where a conductive surface 120 a of the conductive member 120is also shaped as a curved surface.

FIG. 36 is a diagram showing a driver's vehicle 500, and a precedingvehicle 502 that is traveling in the same lane as the driver's vehicle500 according to an example embodiment of the present disclosure.

FIG. 37 is a diagram showing an onboard radar system 510 of the driver'svehicle 500.

FIG. 38A is a diagram showing a relationship between an array antenna AAof the onboard radar system 510 and plural arriving waves k according toan example embodiment of the present disclosure.

FIG. 38B is a diagram showing the array antenna AA receiving the k^(th)arriving wave.

FIG. 39 is a block diagram showing an example embodiment of a vehicletravel controlling apparatus 600 according to the present disclosure.

FIG. 40 is a block diagram showing another example embodiment of thepresent disclosure for the vehicle travel controlling apparatus 600.

FIG. 41 is a block diagram showing an example embodiment of the presentdisclosure of a more specific construction of the vehicle travelcontrolling apparatus 600.

FIG. 42 is a block diagram showing a more detailed example embodiment ofthe present disclosure of the radar system 510 according to thisApplication Example.

FIG. 43 is a diagram showing change in frequency of a transmissionsignal which is modulated based on the signal that is generated by atriangular wave generation circuit 581 according to an exampleembodiment of the present disclosure.

FIG. 44 is a diagram showing a beat frequency fu in an “ascent” periodand a beat frequency fd in a “descent” period according to an exampleembodiment of the present disclosure.

FIG. 45 is a diagram showing an example embodiment of the presentdisclosure in which a signal processing circuit 560 is implemented inhardware including a processor PR and a memory device MD.

FIG. 46 is a diagram showing a relationship between three frequenciesf1, f2 and f3 according to an example embodiment of the presentdisclosure.

FIG. 47 is a diagram showing a relationship between synthetic spectra F1to F3 on a complex plane according to an example embodiment of thepresent disclosure.

FIG. 48 is a flowchart showing the procedure of a process of determiningrelative velocity and distance according to an example embodiment of thepresent disclosure.

FIG. 49 is a diagram concerning a fusion apparatus in which a radarsystem 510 having a slot array antenna and an onboard camera system 700are included according to an example embodiment of the presentdisclosure.

FIG. 50 is a diagram illustrating how placing a millimeter wave radar510 and a camera at substantially the same position within the vehicleroom may allow them to acquire an identical field of view and line ofsight, thus facilitating a matching process according to an exampleembodiment of the present disclosure.

FIG. 51 is a diagram showing an example embodiment of the presentdisclosure for a monitoring system 1500 based on millimeter wave radar.

FIG. 52 is a block diagram showing an example embodiment of the presentdisclosure for a digital communication system 800A.

FIG. 53 is a block diagram showing an example embodiment of the presentdisclosure of a communication system 800B including a transmitter 810Bwhich is capable of changing its radio wave radiation pattern.

FIG. 54 is a block diagram showing an example embodiment of the presentdisclosure of a communication system 800C implementing a MIMO function.

DETAILED DESCRIPTION

Prior to describing example embodiments of the present disclosure,findings that form the basis of the present disclosure will bedescribed.

A ridge waveguide which is disclosed in the aforementioned specificationof U.S. Pat. No. 8,779,995, the specification of U.S. Pat. No.8,803,638, the specification of European Patent Application PublicationNo. 1331688 and H. Kirino and K. Ogawa, “A 76 GHz Multi-Layered PhasedArray Antenna using a Non-Metal Contact Metamaterial Wavegude”, IEEETransaction on Antenna and Propagation, Vol. 60, No. 2, pp. 840-853,February, 2012 and A. Uz. Zaman and P.-S. Kildal, “Ku Band LinearSlot-Array in Ridge Gapwaveguide Technology, EUCAP 2013, 7th EuropeanConference on Antenna and Propagation is provided in a waffle ironstructure which is capable of functioning as an artificial magneticconductor. A ridge waveguide in which such an artificial magneticconductor is utilized based on the present disclosure (which hereinaftermay be referred to as a WRG: Waffle-iron Ridge waveguide) is able torealize an antenna feeding network with low losses in the microwave orthe millimeter wave band. Moreover, use of such a ridge waveguide allowsantenna elements to be disposed with a high density. Hereinafter, anexemplary fundamental construction and operation of such a waveguidestructure will be described.

An artificial magnetic conductor is a structure which artificiallyrealizes the properties of a perfect magnetic conductor (PMC), whichdoes not exist in nature. One property of a perfect magnetic conductoris that “a magnetic field on its surface has zero tangential component”.This property is the opposite of the property of a perfect electricconductor (PEC), i.e., “an electric field on its surface has zerotangential component”. Although no perfect magnetic conductor exists innature, it can be embodied by an artificial structure, e.g., an array ofa plurality of electrically conductive rods. An artificial magneticconductor functions as a perfect magnetic conductor in a specificfrequency band which is defined by its structure. An artificial magneticconductor restrains or prevents an electromagnetic wave of any frequencythat is contained in the specific frequency band (propagation-restrictedband) from propagating along the surface of the artificial magneticconductor. For this reason, the surface of an artificial magneticconductor may be referred to as a high impedance surface.

In the waveguide devices disclosed in the specification of U.S. Pat. No.8,779,995, the specification of U.S. Pat. No. 8,803,638, thespecification of European Patent and H. Kirino and K. Ogawa, “A 76 GHzMulti-Layered Phased Array Antenna using a Non-Metal ContactMetamaterial Wavegude”, IEEE Transaction on Antenna and Propagation,Vol. 60, No. 2, pp. 840-853, February, 2012 and A. Uz. Zaman and P.-S.Kildal, “Ku Band Linear Slot-Array in Ridge Gapwaveguide Technology,EUCAP 2013, 7th European Conference on Antenna and Propagation, anartificial magnetic conductor is realized by a plurality of electricallyconductive rods which are arrayed along row and column directions. Suchrods are projections which may also be referred to as posts or pins.Each of these waveguide devices includes, as a whole, a pair of opposingelectrically conductive plates. One conductive plate has a ridgeprotruding toward the other conductive plate, and stretches of anartificial magnetic conductor extending on both sides of the ridge. Anupper face (i.e., its electrically conductive face) of the ridgeopposes, via a gap, an electrically conductive surface of the otherconductive plate. An electromagnetic wave (signal wave) of a wavelengthwhich is contained in the propagation-restricted band of the artificialmagnetic conductor propagates along the ridge, in the space (gap)between this conductive surface and the upper face of the ridge.

FIG. 1 is a perspective view schematically showing a non-limitingexample of a fundamental construction of such a waveguide device. FIG. 1shows XYZ coordinates along X, Y and Z directions which are orthogonalto one another. The waveguide device 100 shown in the figure includes aplate-like electrically conductive member 110 and a plate shape(plate-like) electrically conductive member 120, which are in opposingand parallel positions to each other. A plurality of electricallyconductive rods 124 are arrayed on the second conductive member 120.

Note that any structure appearing in a figure of the present applicationis shown in an orientation that is selected for ease of explanation,which in no way should limit its orientation when an example embodimentof the present disclosure is actually practiced. Moreover, the shape andsize of a whole or a part of any structure that is shown in a figureshould not limit its actual shape and size.

FIG. 2A is a diagram schematically showing the construction of a crosssection of the waveguide device 100 in FIG. 1, taken parallel to the XZplane. As shown in FIG. 2A, the conductive member 110 has anelectrically conductive surface 110 a on the side facing the conductivemember 120. The conductive surface 110 a has a two-dimensional expansealong a plane which is orthogonal to the axial direction (i.e., the Zdirection) of the conductive rods 124 (i.e., a plane which is parallelto the XY plane). Although the conductive surface 110 a is shown to be asmooth plane in this example, the conductive surface 110 a does not needto be a plane, as will be described later.

FIG. 3 is a perspective view schematically showing the waveguide device100, illustrated so that the spacing between the conductive member 110and the conductive member 120 is exaggerated for ease of understanding.In an actual waveguide device 100, as shown in FIG. 1 and FIG. 2A, thespacing between the conductive member 110 and the conductive member 120is narrow, with the conductive member 110 covering over all of theconductive rods 124 on the conductive member 120.

FIG. 1 to FIG. 3 only show portions of the waveguide device 100. Theconductive members 110 and 120, the waveguide member 122, and theplurality of conductive rods 124 actually extend to outside of theportions illustrated in the figures. At an end of the waveguide member122, as will be described later, a choke structure for preventingelectromagnetic waves from leaking into the external space is provided.The choke structure may include a row of conductive rods that areadjacent to the end of the waveguide member 122, for example.

See FIG. 2A again. The plurality of conductive rods 124 arrayed on theconductive member 120 each have a leading end 124 a opposing theconductive surface 110 a. In the example shown in the figure, theleading ends 124 a of the plurality of conductive rods 124 are on thesame plane. This plane defines the surface 125 of an artificial magneticconductor. Each conductive rod 124 does not need to be entirelyelectrically conductive, so long as it at least includes an electricallyconductive layer that extends along the upper face and the side surfaceof the rod-like structure. Although this electrically conductive layermay be located at the surface layer of the rod-like structure, thesurface layer may be composed of an insulation coating or a resin layerwith no electrically conductive layer existing on the surface of therod-like structure. Moreover, each conductive member 120 does not needto be entirely electrically conductive, so long as it can support theplurality of conductive rods 124 to constitute an artificial magneticconductor. Of the surfaces of the conductive member 120, a face carryingthe plurality of conductive rods 124 may be electrically conductive,such that the electrical conductor electrically interconnects thesurfaces of adjacent ones of the plurality of conductive rods 124.Moreover, the electrically conductive layer of the conductive member 120may be covered with an insulation coating or a resin layer. In otherwords, the entire combination of the conductive member 120 and theplurality of conductive rods 124 may at least include an electricallyconductive layer with rises and falls opposing the conductive surface110 a of the conductive member 110.

On the conductive member 120, a ridge-like waveguide member 122 isprovided among the plurality of conductive rods 124. More specifically,stretches of an artificial magnetic conductor are present on both sidesof the waveguide member 122, such that the waveguide member 122 issandwiched between the stretches of artificial magnetic conductor onboth sides. As can be seen from FIG. 3, the waveguide member 122 in thisexample is supported on the conductive member 120, and extends linearlyalong the Y direction. In the example shown in the figure, the waveguidemember 122 has the same height and width as those of the conductive rods124. As will be described later, however, the height and width of thewaveguide member 122 may have respectively different values from thoseof the conductive rod 124. Unlike the conductive rods 124, the waveguidemember 122 extends along a direction (which in this example is the Ydirection) in which to guide electromagnetic waves along the conductivesurface 110 a. Similarly, the waveguide member 122 does not need to beentirely electrically conductive, but may at least include anelectrically conductive waveguide surface 122 a opposing the conductivesurface 110 a of the conductive member 110. The conductive member 120,the plurality of conductive rods 124, and the waveguide member 122 maybe portions of a continuous single-piece body. Furthermore, theconductive member 110 may also be a portion of such a single-piece body.

On both sides of the waveguide member 122, the space between the surface125 of each stretch of artificial magnetic conductor and the conductivesurface 110 a of the conductive member 110 does not allow anelectromagnetic wave of any frequency that is within a specificfrequency band to propagate. This frequency band is called a “prohibitedband”. The artificial magnetic conductor is designed so that thefrequency of an electromagnetic wave (signal wave) to propagate in thewaveguide device 100 (which may hereinafter be referred to as the“operating frequency”) is contained in the prohibited band. Theprohibited band may be adjusted based on the following: the height ofthe conductive rods 124, i.e., the depth of each groove formed betweenadjacent conductive rods 124; the width of each conductive rod 124; theinterval between conductive rods 124; and the size of the gap betweenthe leading end 124 a and the conductive surface 110 a of eachconductive rod 124.

Next, with reference to FIG. 4, the dimensions, shape, positioning, andthe like of each member will be described.

FIG. 4 is a diagram showing an exemplary range of dimension of eachmember in the structure shown in FIG. 2A. The waveguide device is usedfor at least one of transmission and reception of electromagnetic wavesof a predetermined band (referred to as the “operating frequency band”).In the present specification, λo denotes a representative value ofwavelengths in free space (e.g., a central wavelength corresponding to acenter frequency in the operating frequency band) of an electromagneticwave (signal wave) propagating in a waveguide extending between theconductive surface 110 a of the conductive member 110 and the waveguidesurface 122 a of the waveguide member 122. Moreover, λm denotes awavelength, in free space, of an electromagnetic wave of the highestfrequency in the operating frequency band. The end of each conductiverod 124 that is in contact with the conductive member 120 is referred toas the “root”. As shown in FIG. 4, each conductive rod 124 has theleading end 124 a and the root 124 b. Examples of dimensions, shapes,positioning, and the like of the respective members are as follows.

(1) Width of the Conductive Rod

The width (i.e., the size along the X direction and the Y direction) ofthe conductive rod 124 may be set to less than λm/2. Within this range,resonance of the lowest order can be prevented from occurring along theX direction and the Y direction. Since resonance may possibly occur notonly in the X and Y directions but also in any diagonal direction in anX-Y cross section, the diagonal length of an X-Y cross section of theconductive rod 124 is also preferably less than λm/2. The lower limitvalues for the rod width and diagonal length will conform to the minimumlengths that are producible under the given manufacturing method, but isnot particularly limited.

(2) Distance from the Root of the Conductive Rod to the ConductiveSurface of the Conductive Member 110

The distance from the root 124 b of each conductive rod 124 to theconductive surface 110 a of the conductive member 110 may be longer thanthe height of the conductive rods 124, while also being less than λm/2.When the distance is λm/2 or more, resonance may occur between the root124 b of each conductive rod 124 and the conductive surface 110 a, thusreducing the effect of signal wave containment.

The distance from the root 124 b of each conductive rod 124 to theconductive surface 110 a of the conductive member 110 corresponds to thespacing between the conductive member 110 and the conductive member 120.For example, when a signal wave of 76.5±0.5 GHz (which belongs to themillimeter band or the extremely high frequency band) propagates in thewaveguide, the wavelength of the signal wave is in the range from 3.8934mm to 3.9446 mm. Therefore, λm equals 3.8934 mm in this case, so thatthe spacing between the conductive member 110 and the conductive member120 may be set to less than a half of 3.8934 mm. So long as theconductive member 110 and the conductive member 120 realize such anarrow spacing while being disposed opposite from each other, theconductive member 110 and the conductive member 120 do not need to bestrictly parallel. Moreover, when the spacing between the conductivemember 110 and the conductive member 120 is less than λm/2, a whole or apart of the conductive member 110 and/or the conductive member 120 maybe shaped as a curved surface. On the other hand, the conductive members110 and 120 each have a planar shape (i.e., the shape of their region asperpendicularly projected onto the XY plane) and a planar size (i.e.,the size of their region as perpendicularly projected onto the XY plane)which may be arbitrarily designed depending on the purpose.

Although the conductive surface 120 a is illustrated as a plane in theexample shown in FIG. 2A, example embodiments of the present disclosureare not limited thereto. For example, as shown in FIG. 2B, theconductive surface 120 a may be the bottom parts of faces each of whichhas a cross section similar to a U-shape or a V-shape. The conductivesurface 120 a will have such a structure when each conductive rod 124 orthe waveguide member 122 is shaped with a width which increases towardthe root. Even with such a structure, the device shown in FIG. 2B canfunction as the waveguide device according to an example embodiment ofthe present disclosure so long as the distance between the conductivesurface 110 a and the conductive surface 120 a is less than a half ofthe wavelength λm.

(3) Distance L2 from the Leading End of the Conductive Rod to theConductive Surface

The distance L2 from the leading end 124 a of each conductive rod 124 tothe conductive surface 110 a is set to less than λm/2. When the distanceis λm/2 or more, a propagation mode where electromagnetic wavesreciprocate between the leading end 124 a of each conductive rod 124 andthe conductive surface 110 a may occur, thus no longer being able tocontain an electromagnetic wave. Note that, among the plurality ofconductive rods 124, at least those which are adjacent to the waveguidemember 122 do not have their leading ends in electrical contact with theconductive surface 110 a. As used herein, the leading end of aconductive rod not being in electrical contact with the conductivesurface means either of the following states: there being an air gapbetween the leading end and the conductive surface; or the leading endof the conductive rod and the conductive surface adjoining each othervia an insulating layer which may exist in the leading end of theconductive rod or in the conductive surface.

(4) Arrangement and Shape of Conductive Rods

The interspace between two adjacent conductive rods 124 among theplurality of conductive rods 124 has a width of less than λm/2, forexample. The width of the interspace between any two adjacent conductiverods 124 is defined by the shortest distance from the surface (sidesurface) of one of the two conductive rods 124 to the surface (sidesurface) of the other. This width of the interspace between rods is tobe determined so that resonance of the lowest order will not occur inthe regions between rods. The conditions under which resonance willoccur are determined based by a combination of: the height of theconductive rods 124; the distance between any two adjacent conductiverods; and the capacitance of the air gap between the leading end 124 aof each conductive rod 124 and the conductive surface 110 a. Therefore,the width of the interspace between rods may be appropriately determineddepending on other design parameters. Although there is no clear lowerlimit to the width of the interspace between rods, for manufacturingease, it may be e.g. λm/16 or more when an electromagnetic wave in theextremely high frequency range is to be propagated. Note that theinterspace does not need to have a constant width. So long as it remainsless than λm/2, the interspace between conductive rods 124 may vary.

The arrangement of the plurality of conductive rods 124 is not limitedto the illustrated example, so long as it exhibits a function of anartificial magnetic conductor. The plurality of conductive rods 124 donot need to be arranged in orthogonal rows and columns; the rows andcolumns may be intersecting at angles other than 90 degrees. Theplurality of conductive rods 124 do not need to form a linear arrayalong rows or columns, but may be in a dispersed arrangement which doesnot present any straightforward regularity. The conductive rods 124 mayalso vary in shape and size depending on the position on the conductivemember 120.

The surface 125 of the artificial magnetic conductor that areconstituted by the leading ends 124 a of the plurality of conductiverods 124 does not need to be a strict plane, but may be a plane withminute rises and falls, or even a curved surface. In other words, theconductive rods 124 do not need to be of uniform height, but rather theconductive rods 124 may be diverse so long as the array of conductiverods 124 is able to function as an artificial magnetic conductor.

Each conductive rod 124 does not need to have a prismatic shape as shownin the figure, but may have a cylindrical shape, for example.Furthermore, each conductive rod 124 does not need to have a simplecolumnar shape. The artificial magnetic conductor may also be realizedby any structure other than an array of conductive rods 124, and variousartificial magnetic conductors are applicable to the waveguide device ofthe present disclosure. Note that, when the leading end 124 a of eachconductive rod 124 has a prismatic shape, its diagonal length ispreferably less than λm/2. When the leading end 124 a of each conductiverod 124 is shaped as an ellipse, the length of its major axis ispreferably less than λm/2. Even when the leading end 124 a has any othershape, the dimension across it is preferably less than λm/2 even at thelongest position.

The height of each conductive rod 124 (in particular, those conductiverods 124 which are adjacent to the waveguide member 122), i.e., thelength from the root 124 b to the leading end 124 a, may be set to avalue which is shorter than the distance (i.e., less than λm/2) betweenthe conductive surface 110 a and the conductive surface 120 a, e.g.,λo/4.

(5) Width of the Waveguide Surface

The width of the waveguide surface 122 a of the waveguide member 122,i.e., the size of the waveguide surface 122 a along a direction which isorthogonal to the direction that the waveguide member 122 extends, maybe set to less than λm/2 (e.g. λo/8). If the width of the waveguidesurface 122 a is λm/2 or more, resonance will occur along the widthdirection, which will prevent any WRG from operating as a simpletransmission line.

(6) Height of the Waveguide Member

The height (i.e., the size along the Z direction in the example shown inthe figure) of the waveguide member 122 is set to less than λm/2. Thereason is that, if the distance is λm/2 or more, the distance betweenthe root 124 b of each conductive rod 124 and the conductive surface 110a will be λm/2 or more. Similarly, the height of each conductive rod 124(in particular, any conductive rod 124 that is adjacent to the waveguidemember 122) is also set to less than λm/2.

(7) Distance L1 Between the Waveguide Surface and the Conductive Surface

The distance L1 between the waveguide surface 122 a of the waveguidemember 122 and the conductive surface 110 a is set to less than λm/2. Ifthe distance is λm/2 or more, resonance will occur between the waveguidesurface 122 a and the conductive surface 110 a, which will preventfunctionality as a waveguide. In one example, the distance L1 is λm/4 orless. In order to ensure manufacturing ease, when an electromagneticwave in the extremely high frequency range is to propagate, the distanceL1 is preferably λm/16 or more, for example.

The lower limit of the distance L1 between the conductive surface 110 aand the waveguide surface 122 a and the lower limit of the distance L2between the conductive surface 110 a and the leading end 124 a of eachconductive rod 124 depends on the machining precision, and also on theprecision when assembling the two upper/lower conductive members 110 and120 so as to be apart by a constant distance. When a pressing techniqueor an injection technique is used, the practical lower limit of theaforementioned distance is about 50 micrometers (μm). In the case ofusing an MEMS (Micro-Electro-Mechanical System) technique to make aproduct in e.g. the terahertz range, the lower limit of theaforementioned distance is about 2 to about 3 μm.

In the waveguide device 100 of the above-described construction, asignal wave of the operating frequency is unable to propagate in thespace between the surface 125 of the artificial magnetic conductor andthe conductive surface 110 a of the conductive member 110, butpropagates in the space between the waveguide surface 122 a of thewaveguide member 122 and the conductive surface 110 a of the conductivemember 110. Unlike in a hollow waveguide, the width of the waveguidemember 122 in such a waveguide structure does not need to be equal to orgreater than a half of the wavelength of the electromagnetic wave topropagate. Moreover, the conductive member 110 and the conductive member120 do not need to be interconnected by a metal wall that extends alongthe thickness direction (i.e., in parallel to the YZ plane).

FIG. 5A schematically shows an electromagnetic wave that propagates in anarrow space, i.e., a gap between the waveguide surface 122 a of thewaveguide member 122 and the conductive surface 110 a of the conductivemember 110. Three arrows in FIG. 5A schematically indicate theorientation of an electric field of the propagating electromagneticwave. The electric field of the propagating electromagnetic wave isperpendicular to the conductive surface 110 a of the conductive member110 and to the waveguide surface 122 a.

On both sides of the waveguide member 122, stretches of artificialmagnetic conductor that are created by the plurality of conductive rods124 are present. An electromagnetic wave propagates in the gap betweenthe waveguide surface 122 a of the waveguide member 122 and theconductive surface 110 a of the conductive member 110. FIG. 5A isschematic, and does not accurately represent the magnitude of anelectromagnetic field to be actually created by the electromagneticwave. A part of the electromagnetic wave (electromagnetic field)propagating in the space over the waveguide surface 122 a may have alateral expanse, to the outside (i.e., toward where the artificialmagnetic conductor exists) of the space that is delineated by the widthof the waveguide surface 122 a. In this example, the electromagneticwave propagates in a direction (i.e., the Y direction) which isperpendicular to the plane of FIG. 5A. As such, the waveguide member 122does not need to extend linearly along the Y direction, but may includea bend(s) and/or a branching portion(s) not shown. Since theelectromagnetic wave propagates along the waveguide surface 122 a of thewaveguide member 122, the direction of propagation would change at abend, whereas the direction of propagation would ramify into pluraldirections at a branching portion.

In the waveguide structure of FIG. 5A, no metal wall (electric wall),which would be indispensable to a hollow waveguide, exists on both sidesof the propagating electromagnetic wave. Therefore, in the waveguidestructure of this example, “a constraint due to a metal wall (electricwall)” is not included in the boundary conditions for theelectromagnetic field mode to be created by the propagatingelectromagnetic wave, and the width (size along the X direction) of thewaveguide surface 122 a is less than a half of the wavelength of theelectromagnetic wave.

For reference, FIG. 5B schematically shows a cross section of a hollowwaveguide 130. With arrows, FIG. 5B schematically shows the orientationof an electric field of an electromagnetic field mode (TE₁₀) that iscreated in the internal space 132 of the hollow waveguide 130. Thelengths of the arrows correspond to electric field intensities. Thewidth of the internal space 132 of the hollow waveguide 130 needs to beset to be broader than a half of the wavelength. In other words, thewidth of the internal space 132 of the hollow waveguide 130 cannot beset to be smaller than a half of the wavelength of the propagatingelectromagnetic wave.

FIG. 5C is a cross-sectional view showing an implementation where twowaveguide members 122 are provided on the conductive member 120. Thus,an artificial magnetic conductor that is created by the plurality ofconductive rods 124 exists between the two adjacent waveguide members122. More accurately, stretches of artificial magnetic conductor createdby the plurality of conductive rods 124 are present on both sides ofeach waveguide member 122, such that each waveguide member 122 is ableto independently propagate an electromagnetic wave.

For reference's sake, FIG. 5D schematically shows a cross section of awaveguide device in which two hollow waveguides 130 are placedside-by-side. The two hollow waveguides 130 are electrically insulatedfrom each other. Each space in which an electromagnetic wave is topropagate needs to be surrounded by a metal wall that defines therespective hollow waveguide 130. Therefore, the interval between theinternal spaces 132 in which electromagnetic waves are to propagatecannot be made smaller than a total of the thicknesses of two metalwalls. Usually, a total of the thicknesses of two metal walls is longerthan a half of the wavelength of a propagating electromagnetic wave.Therefore, it is difficult for the interval between the hollowwaveguides 130 (i.e., interval between their centers) to be shorter thanthe wavelength of a propagating electromagnetic wave. Particularly forelectromagnetic waves of wavelengths in the extremely high frequencyrange (i.e., electromagnetic wave wavelength: 10 mm or less) or evenshorter wavelengths, a metal wall which is sufficiently thin relative tothe wavelength is difficult to be formed. This presents a cost problemin commercially practical implementation.

On the other hand, a waveguide device 100 including an artificialmagnetic conductor can easily realize a structure in which waveguidemembers 122 are placed close to one another. Thus, such a waveguidedevice 100 can be suitably used in an array antenna that includes pluralantenna elements in a close arrangement.

When a branching portion for branching the direction of propagation of asignal wave into two or more is introduced in a waveguide member 122 ofthe waveguide device as described above, unwanted reflection of thesignal wave needs to be suppressed. This requires a higher degree ofimpedance matching at the branching portion. Structures for causingbranching in a waveguide are used in transmission lines, such asmicrostrip lines, for example. When a branching portion is introduced ina transmission line such as a microstrip line, since a plurality oftransmission lines exist beyond the branching portion, the impedance asviewed from before the branching portion will be a synthetic impedanceof those of the plurality of transmission lines. Therefore, unless thecharacteristic impedances of the transmission lines are changed, astructure to convert impedance is often introduced in order to establishimpedance matching before and after the branching portion. Such animpedance conversion structure is called an impedance transformer.

FIG. 6A is a diagram schematically showing an example of an impedancetransformer which is used in a microstrip line. The arrows in the figureschematically indicate directions of propagation of signal waves. In amicrostrip line, over a ¼ length of a wavelength λr of a signal wave inthe waveguide, a portion which is broader in width than any adjacentsite (which hereinafter may be referred to as a “broad portion”) is maybe provided. The number of broad portions is not limited to one, and aplurality of broad portions of different widths may also be provided.The length of each broad portion along the direction of the line isλr/4, such that its width increases toward the branching portion. Such astructure is called a λ/4 transformer, which is used in order toestablish impedance matching before and after a branching portion.

On the other hand, a branching portion having a T-shaped structure willresult in a broader transmission line width; therefore, a notch is maybe provided at a branching portion for width adjustment. FIG. 6B is adiagram schematically showing an exemplary structure of a branchingportion in which such a notch is provided. An example of such astructure is disclosed in Kazuaki KAWABATA et al., “Computer Analysis ofMicrowave Planar Circuits by Finite Element Method: Right angle Cornersand Tee Junctions”, Bulletin of the Faculty of Engineering, HokkaidoUniversity, 77: 61-68, for example. By appropriately setting the shapeand size of the notch, signal wave reflection can be suppressed.

A structure as shown in FIG. 6A and FIG. 6B might also be applied to theaforementioned ridge waveguide (WRG) in a similar manner. However,according to a study by the inventors, merely applying a structure asshown in FIG. 6A and FIG. 6B to a WRG will not sufficiently suppresssignal wave reflection. Hereinafter, this problem will be described withreference to FIG. 7 through FIG. 11.

FIG. 7 and FIG. 8A are perspective views schematically showing part ofthe structure of a waveguide device according to comparative examples.FIG. 7 and FIG. 8A show part of a construction of the second conductivemember 120, and a waveguide member 122 and a plurality of conductiverods 124 thereon. Upon these constituent elements, the aforementionedfirst conductive member 110 exists. The waveguide member 122 includes afirst portion 122A extending along the Y direction, and a second portion122B and a third portion 122C extending along the X direction. The firstportion 122A, the second portion 122B, and the third portion 122C areconnected at a branching portion 136 to constitute a T-shaped structure.In the following description, the first portion 122A may be referred toas a “stem”, whereas the second portion 122B and the third portion 122Cmay be referred to as “branches”. The first to third portions 122A to122C will be collectively referred to as the “waveguide member 122”.

In the example of FIG. 8A, the width of the waveguide surface of thewaveguide member 122 at the first portion 122A varies with distance fromthe branching portion 136 so as to present a staircase shape. Within thefirst portion 122A, each portion of identical width has a length alongthe Y direction which is ¼ of a wavelength λr of a signal wave in thewaveguide. At any site, each portion of identical width has a lengthalong the Y direction which is greater than the width of the waveguidesurface. The width of the waveguide surface at the first portion 122Aincreases, in steps, toward the branching portion 136. Such a structurefunctions as the aforementioned λ/4 transformer (impedance transformer).

FIG. 8B is a diagram showing enlarged the structure near the branchingportion 136 in FIG. 8A. The structure of this comparative example cannotsufficiently suppress signal wave reflection at the branching portion136. The inventors infer that this is because capacitive coupling occurson the inward of the branching portion 136 (i.e., between the stem 122Aand the branch 122B, and between the stem 122A and the branch 122C) toresult in excess capacitance components (parasitic capacitance). Thearrows in FIG. 8B schematically indicate directions of electric fieldsbetween the stem 122A and the branches 122B and 122C. Owing tocapacitance components occurring between the inward side surfaces of thebranching portion 136, an electric field as shown in the figure may becreated. In a WRG, it is considered that these capacitance componentsexert a nonnegligible influence on impedance matching. A similar problemalso exists in the construction shown in FIG. 7. Thus, it has been foundthat adequate matching cannot be achieved even if a branching structure,which has been conventionally used in microstrip lines or the like, isapplied to a WRG.

Generally speaking, in order to establish matching between atransmission line having an impedance Z₁ and a transmission line havingan impedance Z₂, an impedance transformer having an impedance Z_(t)expressed as Z_(t)=(Z₁Z₂)^(1/2) may be introduced therebetween. Forexample, in a T-shaped waveguide in which the stem and the two branchesall have an identical characteristic impedance, the impedance of thebranching structure as viewed from the stem is ½ of the impedance of thestem (i.e., Z₂=Z₁/2). Therefore, in such a waveguide, matching can beachieved by setting the impedance of the impedance transformer toZ_(t)=Z₁/2^(1/2)(=Z₁/√ 2).

In order to reduce the characteristic impedance of a transmission line,its capacitance component C may be increased, or its inductancecomponent L may be decreased. In a microstrip line, as described above,an impedance transformer is created by broadening the width of thewaveguide. Also in a WRG, as in the example of FIG. 8A, the an impedancetransformer can be created by broadening the width of the waveguide.However, as described earlier, the influence of parasitic capacitancesoccurring between the inward side surfaces of the branching portion 136may make it difficult to achieve impedance matching. This problem isunique to a WRG, and has never been recognized in conventionaltransmission lines such as microstrip lines.

In a WRG, an effect which is similar or superior to increasing the widthof the waveguide surface can be relatively easily achieved by reducingthe distance between the waveguide surface 122 a of the waveguide member122 and the conductive surface 110 a of the conductive member 110. Theinventors have also studied such structures, but have concluded that,again, the influence of parasitic capacitance unique to a WRG must betaken into consideration.

FIG. 9A is a perspective view schematically showing part of theconstruction of a waveguide device structured so that the distancebetween the waveguide surface 122 a of the waveguide member 122 and theconductive surface 110 a of the conductive member 110 is decreased atimpedance transformers. In this example, unlike in the example of FIG.8A, not the width but the height of the waveguide surface 122 a of thewaveguide member 122 at the first portion 122A is varied in steps.Similarly to varying the width, varying the height also provides aneffect of increasing the capacitance between the waveguide surface 122 aand the conductive surface 110 a of the conductive member 110.Therefore, impedance adjustment is possible through adjusting the heightof the waveguide member 122. Within the first portion 122A of thewaveguide member 122, each portion of identical height has a lengthalong the Y direction which is ¼ of a wavelength λr of a signal wave inthe waveguide. Such a structure also functions as the aforementioned λ/4transformer (impedance transformer).

Note that the length of each impedance transformer is not limited to ¼of the wavelength λr of a signal wave in the waveguide. Under theinfluence of parasitic capacitance and the like associated with the WRG,the optimum length of an impedance transformer may vary around ¼ of λr.However, each impedance transformer has a length which is at least equalto the width of the waveguide surface 122 a, and yet does not exceedthree times the width of the waveguide surface 122 a.

FIG. 9B is a diagram showing enlarged the construction near thebranching portion 136 in FIG. 9A. In this comparative example, too,capacitive coupling occurs between the side surfaces of the firstportion 122A of the waveguide member 122 and the side surfaces of thesecond and third portions 122B and 122C to result in excess capacitancecomponents. Furthermore, in this comparative example, the elevatedheight of the first portion 122A in a region close to the branchingportion 136 is also expected to create an excess capacitance componentbetween the first portion 122A of the waveguide member 122 and theconductive surface 110 a of the first conductive member 110.

FIG. 10 is a diagram schematically showing a cross-sectional structureof the waveguide device in FIG. 9A as taken along a plane which passesthrough the first portion 122A of the waveguide member 122 and isparallel to the YZ plane. The arrows in FIG. 10 schematically indicatedirections of an electric field. As shown in the figure, an impedancetransformer 138 of the first portion 122A of the waveguide member 122has a top surface which is more elevated from any adjacent site, andpresumably for this reason, capacitive coupling occurs between its sidesurface or end face and the conductive surface 110 a of the conductivemember 110. The inventors infer that a resultant capacitance componentfrom this exerts a nonnegligible influence on impedance matching,similarly to the aforementioned capacitance components between theinward side surfaces of the branching portion 136.

FIG. 11 is a diagram showing an equivalent circuit of the waveguidestructure in FIG. 9A. As mentioned above, at the branching portion 136,capacitive coupling occurs between the side surface of the first portion122A of the waveguide member and the side surfaces of the second andthird portions 122B and 122C. Consequently, excess capacitancecomponents C1 are added to the existing inductance component L0, asshown in FIG. 11. Furthermore, capacitive coupling occurs between anupper portion of the side surface or end face of the leading end of thefirst portion 122A of the waveguide member 122 and the conductivesurface 110 a of the conductive member 110. Consequently, an excesscapacitance component C2 is added as shown in FIG. 11. These capacitancecomponents C1 and C2 are considered to be one of the causes of thereduced degree of impedance matching at the branching portion 136.

Based on the above thoughts, as will be described in detail below, theinventors have succeeded in further enhancing the degree of impedancematching at a branching portion in a waveguide member, by improving thestructure of the branching portion. The enhanced degree of impedancematching provides an improved propagation efficiency, and thus awaveguide device with less noise. It also becomes possible to enhancethe performance of an antenna device that includes such a waveguidedevice. For example, establishment of impedance matching suppressessignal wave reflection, whereby power losses can be reduced, and a phasedisturbance in the propagating electromagnetic wave can be suppressed.Therefore, in the context of communications, deteriorations in thecommunicated signals can be reduced, and in the context of radar, theaccuracy of distance or direction-of-arrival estimation can be improved.

Hereinafter, more specific exemplary constructions for waveguide deviceand antenna devices according to example embodiments of the presentdisclosure will be described. Note however that unnecessarily detaileddescriptions may be omitted. For example, detailed descriptions on whatis well known in the art or redundant descriptions on what issubstantially the same constitution may be omitted. This is to avoidlengthy description, and facilitate the understanding of those skilledin the art. The accompanying drawings and the following description,which are provided by the inventors so that those skilled in the art cansufficiently understand the present disclosure, are not intended tolimit the scope of claims. In the present specification, identical orsimilar constituent elements are denoted by identical referencenumerals.

<Waveguide Device> Example Embodiment 1

FIG. 12A is a perspective view schematically showing part of thestructure of a waveguide device according to Example Embodiment 1 of thepresent disclosure. FIG. 12B is an upper plan view showing the waveguidedevice of FIG. 12A as viewed from the +Z direction. FIG. 12C is adiagram showing the waveguide device of FIG. 12A as viewed from the +Ydirection. FIGS. 12A through 12C only show a portion close to abranching portion 136 of a waveguide member 122 in illustrative manners.In actuality, the conductive member 120, the waveguide member 122, andplural conductive rods 124 may also exist in the surroundings of theportion that is shown in the figure. This waveguide device furtherincludes a conductive member 110 (see FIG. 1, etc.) covering over thewaveguide member 122 and the plurality of conductive rods 124. In thepresent specification, the conductive member 110 may be referred to asthe “first conductive member”, and the conductive member 120 may bereferred to as the “second conductive member” or a “further conductivemember”.

The waveguide member 122 has: a waveguide surface 122 a opposing theconductive surface 110 a of the conductive member 110 and having astripe shape (also referred to as a “strip shape”); and anelectrically-conductive side surface 122 b that connects to thewaveguide surface 122 a. In the present specification, a “stripe shape”means a shape which is defined by a single stripe, rather than a shapeconstituted by stripes. Not only shapes that extend linearly in onedirection, but also any shape that bends or branches along the way isalso encompassed by a “stripe shape”. In the case where any portion thatundergoes a change in height or width is provided on the waveguidesurface 122 a, it still falls under the meaning of “stripe shape” solong as the shape includes a portion that extends in one direction asviewed in the normal direction of the waveguide surface 122 a.

On both sides of the waveguide member 122, stretches of artificialmagnetic conductor including a plurality of conductive rods 124 extend.The waveguide member 122 includes: a first portion 122A extending in onedirection (which in the present example embodiment is the Y direction);and second and third portions 122B and 122C extending in mutuallydifferent directions (which in the present example embodiment are the +Xdirection and the −X direction) from one end of the first portion 122A.In the following description, the first portion 122A may be referred toas a “stem”, whereas the second and third portions 122B and 122C mayeach be referred to as a “branch”. In the present example embodiment,the waveguide member 122 includes two branches. The waveguide member 122may include three or more branches. In other words, the waveguide member122 may include at least two branches.

The waveguide member 122 according to the present example embodiment hasa recess (or depression) 135 at the position of the branching portion136. The gap between the waveguide surface 122 a of the waveguide member122 and the conductive surface 110 a of the conductive member 110 islocally enlarged at the recess 135. Of a waveguide that is defined bythe waveguide surface 122 a, the conductive surface 110 a, and theartificial magnetic conductor, any site presenting a locally enlargedgap will be referred to as a “gap enlargement”. At least a part of thebranching portion 136, which is a junction where the first portion 122Aof the waveguide member 122 becomes joined with the two branches (thesecond portion 122B and the third portion 122C), overlaps the gapenlargement as seen through in a direction perpendicular to theconductive surface 110 a.

As shown in FIG. 12C, given a width x of the recess 135 along the Xdirection and a difference z between the height of the waveguide surface122 a from the root of the waveguide member 122 and the height of thebottom of the recess 135, x is greater than z. As will be describedlater in detail, the recess may alternatively be made in the conductivesurface 110 a of the conductive member 110. FIG. 19 shows an exemplarystructure in which a gap enlargement is realized by a recess 142 that ismade in the conductive surface 110 a of the conductive member 110. Inthis structure, given a width x of the recess 142 along the X directionand a depth z of the bottom of the recess 142 relative to any site onthe conductive surface 110 a that is adjacent to the recess 142, x isgreater than z. In the case where recesses are made in both thewaveguide surface 122 a and the conductive surface 110 a, z is a sum ofthe depth of the bottom of the recess in the waveguide surface 122 arelative to any site around the recess and the depth of the bottom ofthe recess in the conductive surface 110 a relative to any site aroundthe recess.

Now, with reference to FIG. 12D and FIG. 12E, the junction (branchingportion 136) according to the present example embodiment will bedescribed. FIG. 12D is a view exclusively showing the waveguide member122, out of the waveguide structure shown in FIG. 12B. FIG. 12E is avariant of the waveguide structure shown in FIG. 12D. The waveguidemember 122 shown in FIG. 12E differs from the waveguide member 122 ofFIG. 12D in that the first portion 122A intersects the second portion122B and the third portion 122C at an angle which is not 90 degrees.Note that an implementation where the first portion 122A intersectseither one of the second portion 122B and the third portion 122C at anangle which is not 90 degrees may also be a variant of the presentexample embodiment. The recess 135 is omitted from illustration in FIG.12D and FIG. 12E. In the present disclosure, the junction (branchingportion 136) is defined as, as illustrated in FIG. 12D and FIG. 12E, aregion that is surrounded by imaginary extensions of an edge of thewaveguide surface of the first portion, an edge of the waveguide surfaceof one branch, and an edge of the waveguide surface of the other branch.This region corresponds to the portion that is shown hatched in thefigure. In FIG. 12B, the entire junction (branching portion 136) islocated in a gap enlargement. In the case where there are three or morebranches, a junction may also be similarly defined.

In the present example embodiment, the conductive surface 110 a opposingthe waveguide surface 122 a is flat. Therefore, the position of the gapenlargement as seen through in a direction perpendicular to theconductive surface 110 a coincides with the position of the recess 135.In the case where the conductive surface 110 a is not flat, however, theposition of the gap enlargement as seen through in a directionperpendicular to the conductive surface 110 a does not necessarilycoincide with the position of the recess 135. Instead of or in additionto the recess 135 in the waveguide surface 122 a, a recess may be madein the conductive surface 110 a. So long as at least one of thewaveguide surface 122 a and the conductive surface 110 a has a recess inthe junction, a gap enlargement is created at that position.

In the present example embodiment, the dimension of the gap enlargementalong the width direction of the first portion 122A of the waveguidemember 122 is greater than the width of the first portion 122A. Herein,the width direction of the first portion 122A refers to the X direction,which is perpendicular to the Y direction (along which the first portion122A extends). The dimension of the gap enlargement along the Xdirection may be equal to or less than the width of the first portion122A.

In the present example embodiment, in the waveguide member 122, thefirst portion 122A intersects the second portion 122B and the thirdportion 122C at angles of substantially 90 degrees at the branchingportion 136, thus constituting a T-shaped branching structure. Thesecond portion 122B and the third portion 122C extend in mutuallyopposite directions from one end of the first portion 122A. Thedirection that the first portion 122A extends may not be orthogonal tothe directions that the second and third portions 122B and 122C extend.Moreover, the second portion 122B and the third portion 122C may notextend in mutually opposite directions from one end of the first portion122A. For example, a Y-shaped structure may be adopted such that bendingby an angle which is greater than 90 degrees occurs from the firstportion 122A of the waveguide member 122 to the second portion 122B andthat bending by an angle which is greater than 90 degrees also occursfrom the first portion 122A to the third portion 122C. The bending anglefrom the first portion 122A to the second portion 122B and the bendingangle from the first portion 122A to the third portion 122C do not needto be equal. Moreover, although the example shown in FIG. 12Aillustrates that the second portion 122B and the third portion 122Cextend in mutually opposite directions from the branching portion 136,such a construction is not a limitation. The first portion 122A and thesecond portion 122B, or the first portion 122A and the third portion122C, may extend in mutually opposite directions from the branchingportion 136.

In the present example embodiment, the size of the gap between thewaveguide surface 122 a and the conductive surface 110 a is greater atthe gap enlargement than at any site on the waveguide that is adjacentto the gap enlargement, and is smaller than the distance between theconductive surface 110 a and a root 122D of the waveguide member 122. Inthe present example embodiment, the root 122D of the waveguide member122 refers to the portion at which the waveguide member 122 and theconductive member 120 are connected; however, this structure is notlimiting. In the case where the waveguide member 122 is not connected tothe conductive member 120, as in a structure shown in FIG. 34B describedlater, the face of the waveguide member 122 that is opposed to theconductive member 120, i.e., the opposite face to the waveguide surface,may be referred to as the root of the waveguide member. In the presentdisclosure, the size of the gap of a gap enlargement means a maximumvalue of the size of the gap at that gap enlargement. For example, inthe case where a bowl-shaped recess which exists in the waveguidesurface 122 a constitutes a gap enlargement, the distance between therecess and the conductive surface at the deepest position of the bowlshape defines the size of the gap.

In the present example embodiment, an enhanced degree of impedancematching can be attained by providing a gap enlargement at the positionof the branching portion 136. Hereinafter, this effect will bedescribed.

FIG. 13 is a diagram showing an equivalent circuit of the ridgewaveguide according to the present example embodiment. In the presentexample embodiment, the waveguide member 122 has a recess 135 in aregion containing a branching portion 136. This structure is equivalentto a structure in which an inductance component L1 is added in parallelto a capacitance component C1 that is associated with the closenessbetween the electrically-conductive side surface of the stem of thewaveguide member 122 and the electrically-conductive side surface ofeach of the two branches. This allows each capacitance component C1occurring from bending at the branching portion 136 to be canceled withthe inductance component L1. The magnitude of the inductance componentL1 depends on the shape, size, and position of the recess 135.Therefore, the shape, size, and position of the recess 135 may bedesigned so that the inductance component L1 will cancel the unwantedcapacitance component C1 at the branching portion 136.

With the above construction, the degree of impedance matching at thebranching portion 136 is improved, whereby unwanted reflection of signalwaves can be suppressed.

FIG. 14A and FIG. 14B are diagrams showing an implementation where animpedance matching structure is provided for the first portion 122A ofthe waveguide member 122. FIG. 14A shows an exemplary waveguide devicehaving a staircase-shaped impedance matching structure, as in thecomparative example shown in FIG. 9A. FIG. 14B shows an exemplarywaveguide device having an impedance matching structure such that thewidth of the waveguide surface 122 a increases toward the branchingportion 136, as in the comparative example shown in FIG. 8A.

An impedance transformer may be provided for at least one of: thewaveguide surface 122 a of the first portion 122A; and the conductivesurface 110 a opposing the waveguide surface 122 a of the first portion122A. In the examples of FIG. 14A and FIG. 14B, two impedancetransformers 138A and 138B are provided on the waveguide surface 122 a.Each impedance transformer allows the capacitance between the waveguidesurface 122 a and the conductive surface 110 a to be increased relativeto any adjacent site. In the example of FIG. 14A, each impedancetransformer reduces the distance between the waveguide surface 122 a andthe conductive surface 110 a relative to any adjacent site. In theexample of FIG. 14B, each impedance transformer enlarges the width ofthe waveguide surface 122 a relative to any adjacent site. The length Lof each of the impedance transformers 138A and 138B as measured alongthe direction that the first portion 122A extends (i.e., the Ydirection) from an end of the first portion 122A adjoining the branchingportion 136 is set to a value which is equal to or greater than thewidth of the waveguide surface 122 a.

FIG. 15A and FIG. 15B are diagrams showing other variants of the presentexample embodiment. In the example shown in FIG. 15A, the junction(branching portion 136) is contained in a recess 135 (gap enlargement)as seen through in a direction perpendicular to the conductive surface110 a. In the example shown in FIG. 15B, the recess 135 as arectangular-shape gap enlargement is provided in a central portion ofthe branching portion 136 of the waveguide member 122, without reachingthe edge of any of the first portion 122A, the second portion 122B, orthe third portion 122C. In other words, in the example of FIG. 15B, asseen through in a direction perpendicular to the conductive surface 110a, the edge of the recess 135 (gap enlargement) is located inside theedge of the first portion 122A and the edges of the respective branches.In the variants shown in FIG. 15A and FIG. 15B, the wall surface of therecess 135 has a staircase shape. Such structures similarly provideimpedance matching as do the above-described structures. Moreover, therecess 135 may be structured so that its wall surface is monotonicallyinclined toward the bottom of the recess 135.

FIG. 16A and FIG. 16B are diagrams showing still other variants. In theexamples shown in FIG. 16A and FIG. 16B, at a junction where first tothird portions 122A, 122B and 122C are joined with one another, thewaveguide member 122 has a recess 139 reaching the waveguide surface 122a (which may hereinafter be referred to as a “first recess”) on a sidesurface 122 s opposite to the first portion 122A. As viewed in adirection perpendicular to the waveguide surface 122 a or the conductivesurface 110 a, the recess 139 overlaps the gap enlargement.

Adopting such structures further enhances the degree of impedancematching.

Hereinafter, with reference to FIG. 17A and FIG. 17B, it will bedescribed how the construction according to the present exampleembodiment improves the degree of impedance matching at the branchingportion 136 of the waveguide member 122.

The inventors have clarified through simulations that the constructionaccording to the present example embodiment provides an improved degreeof impedance matching as compared to the constructions of comparativeexamples (FIG. 7, FIG. 8A and FIG. 9A) where no gap enlargement existsin the branching portion. Herein, the degree of impedance matching isrepresented by an input reflection coefficient. An input reflectioncoefficient is a coefficient which represents a ratio of the intensityof a reflected wave to the intensity of an input wave, indicating themagnitude of return loss. It can be said that, the lower the inputreflection coefficient is, the higher the degree of impedance matchingis.

In this simulation, while setting various parameters to appropriatevalues, an input reflection coefficient S that resulted when anelectromagnetic wave was propagated toward the branching portion 136 wasmeasured as examples, regarding each of the construction of thecomparative example shown in FIG. 9A and the construction of the exampleembodiment illustrated in FIG. 14A.

FIG. 17A and FIG. 17B are graphs showing results of this simulation.FIG. 17A shows frequency dependence of the input reflection coefficient(unit: dB) in the construction of the comparative example shown in FIG.9A. FIG. 17B shows frequency dependence of the input reflectioncoefficient (unit: dB) in the example embodiment illustrated in FIG.14A. As can be seen from FIG. 17A and FIG. 17B, at any frequency, thereturn loss is kept lower in the construction of FIG. 14A than in theconstruction of the comparative example. Moreover, in a broad frequencyrange from 67 GHz to 81 GHz, a relatively low return loss of −20 dB orless is realized. In UWB, for which a license is not a requisite, abandwidth accounting for 5% of the used frequency is supposed to berequired. It has been confirmed that the construction according to thepresent example embodiment achieves low losses across a bandwidth whichis far greater than this bandwidth.

The above structure is likely to be easier to manufacture than is thestructure disclosed in A. Uz. Zaman and P.-S. Kildal, “Ku Band LinearSlot-Array in Ridge Gapwaveguide Technology, EUCAP 2013, 7th EuropeanConference on Antenna and Propagation. In A. Uz. Zaman and P.-S. Kildal,“Ku Band Linear Slot-Array in Ridge Gapwaveguide Technology, EUCAP 2013,7th European Conference on Antenna and Propagation, in order to enhancethe degree of impedance matching at a branching portion, the waveguidemember is notched so that the width of its waveguide surface is locallynarrowed. Such structure is commonplace in microstrip lines, and isintroduced in A. Uz. Zaman and P.-S. Kildal, “Slot Antenna in Ridge GapWaveguide Technology,” 6th European Conference on Antennas andPropagation, Prague, March, 2012 and the like. Since a microstrip lineis a metal foil that is in tight contact with a substrate, forming astructure featuring a locally-narrowed microstrip line does not presentmuch of a problem. On the other hand, when such structure is applied tothe waveguide member of a WRG, since the waveguide member is going to bea ridge-shaped member with a height which is around ¼ of the wavelength,a site having an extremely narrowed width and a comparatively highheight with respect to its width will locally emerge. Such anarrow-widthed site very often makes it difficult to obtain a stableshape in mass production utilizing casting, plastic working, injectionmolding, or other production processes. In the case of manufacture bycutting, cutting a narrow-widthed site out of a waveguide member oftenrequires a cautious cutting.

The branching portion according to the present disclosure does notnecessarily require narrowing of the width of the waveguide member. Whenthe waveguide surface is to be recessed, the processing will be in thedirection of lowering the height of the waveguide member, and thus thewaveguide member can be easily formed. When a conductive surface is tobe recessed, there is no need to alter the shape of the waveguidemember, and all that is necessary is to cause the flat conductivesurface to be recessed. In either case, the processing is easy, and massproduction is facilitated in particular.

As necessary, a site featuring a locally-narrowed width of the waveguidemember and a gap enlargement may be used in combination. Although mademore difficult by the formation of a narrow-widthed portion, manufacturewould still be possible.

Example Embodiment 2

FIG. 18A is a perspective view schematically showing part of thestructure of a waveguide device according to Example Embodiment 2 of thepresent disclosure. FIG. 18B is an upper plan view showing the waveguidedevice of FIG. 18A as viewed along the Z direction. In the presentexample embodiment, the waveguide member 122 includes a second portion122B, a third portion 122C, and a fourth portion 122D (eachcorresponding to a “branch”), which extend in respectively differentdirections from one end of the first portion 122A. That is, thewaveguide member 122 has three branches. The second portion 122B and thethird portion 122C extend from the branching portion 136 in directionsthat are 180 degrees apart (which in the present example embodiment arethe +X direction and the −X direction). The first portion 122A and thefourth portion 122D extend from the branching portion 136 in mutuallydifferent directions (which in the present example embodiment are the +Ydirection and the −Y direction). In the waveguide member 122, the firstportion 122A and fourth portion 122D intersect the second portion 122Band third portion 122C at angles of 90 degrees in the branching portion136, thus constituting a cross-shaped branching structure. Note that theangle constituted by the direction that the first and fourth portions122A and 122D extend and the direction that the second and thirdportions 122B and 122C extend is not limited to 90 degrees. Moreover,the second and third portions 122B and 122C may not extend in mutuallyopposite directions from one end of the first portion 122A. Furthermore,the angle constituted by the fourth portion 122D and the first portion122A is not limited to 180 degrees.

A recess 135 is made at the junction at which the first portion 122A,the second portion 122B, the third portion 122C, and the fourth portion122D are joined with one another, i.e., the branching portion 136.Similarly to Example Embodiment 1, the recess 135 improves the degree ofimpedance matching at the branching portion 136.

According to the present example embodiment, a signal wave that haspropagated along the first portion 122A branches out into three, andpropagates thereafter. The recess 135 being provided at the branchingportion suppresses signal wave reflection upon branching. The number ofbranches from the waveguide member 122 may be four or more. Thedirection that each branch extends may also be arbitrarily selected.

In the present example embodiment, impedance transformers similar tothat shown in the example of FIG. 14A are provided for the first portion122A; however, a construction from which impedance transformers areomitted may also be possible. Alternatively, impedance transformers of aconstruction similar to that of FIG. 14B may be provided. In the presentdisclosure, impedance transformers of the first portion 122A are notessential elements.

Example Embodiment 3

FIG. 19 is a perspective view schematically showing part of thestructure of a waveguide device according to Example Embodiment 3 of thepresent disclosure. In FIG. 19, elements which are hidden by theconductive member 110 are indicated with dotted lines. In the presentexample embodiment, a gap enlargement is realized by a recess 142 madein the conductive surface 110 a of the conductive member 110. Moreover,when the waveguide device is seen through in a direction perpendicularto the conductive surface 110 a (the −Z direction), the region in whichthe recess 142 exists covers the entire junction (branching portion 136)of the waveguide member. In other words, as seen through in a directionperpendicular to any site on the conductive surface 110 a that is aroundthe gap enlargement, the entire junction is located inside the gapenlargement. No recess is made in the waveguide surface 122 a of thewaveguide member 122.

In the construction according to the present example embodiment, too, agap enlargement is created in a position overlapping the branchingportion 136. This allows less increase in capacitance at the branchingportion, and improves the degree of impedance matching. In FIG. 19, thewidth along the X direction and the width along the Y direction of therecess 142 are respectively greater than the width along the X directionand the width along the Y direction of the junction 136 of the waveguidemember. As a result, even if the relative positions of the firstconductive member 110 and the second conductive member 120 are offset ina direction along the conductive surface 110 a, it is still easy tomaintain a state where the recess 142 covers the entire junction 136. Asa result, the degree of impedance matching can be stably improved.

In addition to the construction according to the present exampleembodiment, a recess may be made also in the branching portion 136 ofthe waveguide member 122. Moreover, an impedance matching structure asshown in FIG. 14A or FIG. 14B may be provided for the first portion122A. With any such construction, the effect of impedance matching willbe further improved.

Next, variants of Example Embodiments 1 to 3 will be described.

FIG. 20A is a perspective view schematically showing part of thestructure of a waveguide device according to a variant of ExampleEmbodiment 1. FIG. 20B is an upper plan view showing the waveguidedevice of FIG. 20A as viewed from the +Z direction. In this variant, thedimension of the recess 135 along the X direction is equal to the widthof the first portion 122A. In other words, the dimension of the gapenlargement along the width direction of the first portion 122A is equalto the width of the first portion 122A. A structure where the dimensionof the gap enlargement along the width direction of the first portion122A is equal to the width of the first portion 122A is applicable toExample Embodiments 2 and 3 as well.

FIG. 21A is a perspective view schematically showing part of thestructure of a waveguide device according to another variant of ExampleEmbodiment 1. FIG. 21B is an upper plan view showing the waveguidedevice of FIG. 21A as viewed from the +Z direction. In this variant, thedimension of the recess 135 along the X direction is smaller than thewidth of the first portion 122A. In other words, the dimension of thegap enlargement along the width direction of the first portion 122A issmaller than the width of the first portion 122A. A structure where thedimension of the gap enlargement along the width direction of the firstportion 122A is smaller than the width of the first portion 122A isapplicable to Example Embodiments 2 and 3 as well.

The gap enlargement according to any of these variants has a smallergeometric area as seen through in the +Z direction than that of the gapenlargement according to the example embodiment shown in FIG. 12A. Inthe structure of FIG. 20A, as seen through from the +Z direction, thegap enlargement and the junction are identical in geometric area andshape. In the structure of FIG. 21A, as seen through from the +Zdirection, the gap enlargement only accounts for a part of the junction.Therefore, as compared to the aforementioned example embodiment, thesevariants provide little effect of canceling the capacitance between theside surface of the first portion 122A and the side surfaces of thesecond and third portions 122B and 122C of the waveguide member 122.However, the degree of impedance matching is still improved as comparedto any construction where a gap enlargement is not provided. In the casewhere such a small gap enlargement is provided, as in e.g. ExampleEmbodiment 4 to be described later, it will be effective to provide arecess reaching the waveguide surface 122 a on a side surface of atleast one of the second portion 122B and the third portion 122C, thisside surface connecting to the first portion 122A. By providing such arecess near the branching portion 136, the degree of impedance matchingcan be further enhanced, as will be described later.

Example Embodiment 4

FIG. 22A is a perspective view schematically showing part of thestructure of a waveguide device according to Example Embodiment 4 of thepresent disclosure. FIG. 22B is an upper plan view showing the waveguidedevice of FIG. 22A as viewed from the +Z direction. In the presentexample embodiment, the waveguide member 122 has two recesses (ordepressions) 137 on side surfaces near the branching portion 136.Otherwise, its construction is similar to the construction shown in FIG.14B.

FIG. 23A is an upper plan view showing enlarged only the waveguidemember 122 in the structure shown in FIG. 22A. In the present exampleembodiment, each of the second portion 122B and the third portion 122Cof the waveguide member 122 has a recess 137 on its side surface thatconnects to the first portion 122A. Each recess 137 has asemicylindrical shape extending along a direction (the Z direction)which is perpendicular to the waveguide surface 122 a, and reaches thewaveguide surface 122 a (top surface). Because of the recesses 137, thedistance between the side surface of the first portion 122A of thewaveguide member and the side surfaces of the second portion 122B andthe third portion 122C is increased, thereby suppressing unwantedcapacitance components. Note that, without being limited to the shapeshown, the recesses 137 may take a variety of shapes as will bedescribed below. Although the present example embodiment illustratesthat the two recesses 137 reach the root of the waveguide member 122(i.e., the portion at which the waveguide member 122 and the secondconductive member 120 are connected), one or both of these may not reachthe root. The recesses 137 may be formed only in upper portions that arecloser to the waveguide surface 122 a.

The waveguide device of the present example embodiment is used topropagate electromagnetic waves of a predetermined band thataccommodates electromagnetic waves having a wavelength λo in free space.The predetermined band may be a band which is defined by a range offrequencies belonging to the millimeter waves (about 30 GHz to about 300GHz), for example. The wavelength λo may be a wavelength (centralwavelength) corresponding to the center frequency of such a band, forexample. Given that an electromagnetic wave having a wavelength λo infree space has a wavelength λr when propagating in a waveguide extendingbetween the conductive surface 110 a of the conductive member 110 andthe waveguide surface 122 a of the waveguide member 122, the firstportion 122A of the waveguide member 122 includes an impedancetransformer 138A (which increases the capacitance of the waveguide)spanning a length of λr/4 from one end that is closer to the branchingportion 136. The waveguide member 122 in the present example embodimentfurther includes another impedance transformer 138B spanning a length ofλr/4 adjoining the impedance transformer 138A.

Each impedance transformer 138A, 138B in the present example embodimentis a broad portion of the waveguide member 122 that is greater in widththan any adjacent site. The impedance transformer 138A, which is thecloser one to the branching portion 136, has a greater width than thewidth of the other impedance transformer 138B.

Although the present example embodiment illustrates that the number ofimpedance transformers is two, there may be one, or three or moreimpedance transformer(s). Without being limited to a broad portion, eachimpedance transformer may be a protrusion which makes the distancebetween the conductive surface 110 a and the waveguide surface 122 asmaller at the waveguide member 122 than at any adjacent site. Itsuffices if each impedance transformer is greater in at least one ofheight and width than any adjacent site.

As shown in FIG. 23A, each of the two recesses 137 is provided near oneend of the first portion 122A of the waveguide member 122. Morespecifically, as viewed from a direction which is perpendicular to thewaveguide surface 122 a, the distance a from a point of intersection Pbetween the side surface of the first portion 122A of the waveguidemember 122 and the side surface of the second portion 122B to the centerof the recess 137 along the X direction (i.e., the direction that thesecond portion 122B extends) is shorter than the length d of the recess137 along this direction. The relationship between distance a and lengthd similarly applies to the recess 137 in the side surface of the thirdportion 122C of the waveguide member 122. In other words, as viewed froma direction which is perpendicular to the waveguide surface 122 a, thedistance from a point of intersection between the side surface of thefirst portion 122A and the side surface of the third portion 122C to thecenter of the recess 137 in the third portion 122C is shorter than thelength of the recess 137 along the direction that the third portion 122Cextends.

Although the present example embodiment illustrates that the firstportion 122A of the waveguide member 122 is continuous with an end ofthe recess 137 at the point P, this example is not a limitation. Forinstance, as shown in FIG. 23B, the end of the recess 137 may be remotedfrom the point of intersection P between the side surface of the firstportion 122A of the waveguide member 122 and the side surface of thesecond portion 122B. The same also applies to the recess 137 in thethird portion 122C. Also in this case, a sufficient effect can beachieved so long as a<d is satisfied.

In the present example embodiment, too, the number of branches is notlimited to two. FIG. 24 is an upper plan view showing a waveguide devicewhich includes a waveguide member 122 having three branches as viewedfrom the +Z direction. The waveguide member 122 includes a secondportion 122B, a third portion 122C, and a fourth portion 122D (eachcorresponding to a “branch”), which extend in respectively differentdirections from one end of the first portion 122A. The second portion122B and the third portion 122C extend from the branching portion 136 indirections that are 180 degrees apart (which in the present exampleembodiment are the +X direction and the −X direction). The first portion122A and the fourth portion 122D extend from the branching portion 136in mutually different directions (which in the present exampleembodiment are the +Y direction and the −Y direction). In the waveguidemember 122, the first portion 122A and fourth portion 122D intersect thesecond portion 122B and third portion 122C at angles of 90 degrees inthe branching portion 136, thus constituting a cross-shaped branchingstructure. Note that the angle constituted by the direction that thefirst and fourth portions 122A and 122D extend and the direction thatthe second and third portions 122B and 122C extend is not limited to 90degrees. Moreover, the second and third portions 122B and 122C may notextend in mutually opposite directions from one end of the first portion122A. Furthermore, the angle constituted by the fourth portion 122D andthe first portion 122A is not limited to 180 degrees.

In the present example embodiment, the waveguide member 122 has a recess137 in each of: a site at which a side surface of the first portion 122Ameets a side surface of the second portion 122B; and a site at which aside surface of the first portion 122A meets a side surface of the thirdportion 122C. Moreover, the waveguide member 122 has a recess 137 ineach of: a site at which a side surface of the fourth portion 122D meetsa side surface of the second portion 122B; and a site at which a sidesurface of the fourth portion 122D meets a side surface of the thirdportion 122C. Each recess 137 extends along a direction (the Zdirection) which is perpendicular to the waveguide surface 122 a, andreaches the waveguide surface 122 a (top surface). Moreover, each recess137 has a circular arc shape in a cross section that is perpendicular tothe Z direction (which may hereinafter be referred to as a “horizontalcross section”). The shape of each recess 137 in a horizontal crosssection may be different from a circular arc shape, e.g., a combinationof a circular arc and straight lines extending from the ends of thecircular arc. Thus, a horizontal cross section of each recess 137 mayhave a variety of shapes.

Thus, in the present example embodiment, each of the second portion 122Band the third portion 122C of the waveguide member 122 has a recess 137at its side surface closer to the impedance transformer 138A in thefirst portion 122A, the recesses 137 reaching the waveguide surface 122a. This structure is equivalent to a structure where an inductancecomponent L1 is added in parallel to each capacitance component C1 thatis associated with the closeness between electrically-conductive sidesurfaces at the branching portion 136. Therefore, although the ridgewaveguide shown in FIG. 22A has an equivalent circuit construction whichis similar to the equivalent circuit shown in FIG. 13, the addedinductance component L1 is even greater. This makes it even easier tocancel with the inductance component L1 each capacitance component C1occurring from bending at the branching portion 136. The magnitude ofthe added inductance component L1 depends on the shape, size, andposition of each recess 137. Therefore, the shape, size, and position ofeach recess 137 may be designed so that the inductance component L1 willcancel the unwanted capacitance component C1 at the branching portion136. Although the construction of FIG. 22A is discussed herein, similareffects will also be obtained in constructions other than that of FIG.22A.

FIG. 25A is a perspective view showing part of the structure of awaveguide device according to still another variant of the presentexample embodiment. FIG. 25B is an upper plan view showing the structureof FIG. 25A as viewed from the +Z direction. In the present exampleembodiment, the two impedance transformers 138A and 138B in the firstportion 122A of the waveguide member 122 are realized by a structurewith varying height, rather than width, of the waveguide surface 122 a.Such structure also provides similar effects.

With the above construction, the degree of impedance matching at thebranching portion 136 is improved, and unwanted reflection of signalwaves can be suppressed.

Example Embodiment 5

FIG. 26A is a perspective view showing part of the structure of awaveguide device according to Example Embodiment 5 of the presentdisclosure. FIG. 26B is an upper plan view showing the structure of FIG.26A as viewed from the +Z direction. In the present example embodiment,the two impedance transformers 138A and 138B in the first portion 122Aof the waveguide member 122 are realized by a structure with varyingheight, rather than width, of the waveguide surface 122 a. Moreover, ona side surface opposite from the first portion 122A, the waveguidemember 122 has a recess 139 at the junction (branching portion 136)where the first to third portions 122A to 122C are joined with oneanother, the recess 139 reaching the waveguide surface 122 a. In thepresent specification, the recess 139 in the branching portion 136 maybe referred to as a “first recess”, the recess 137 in the second portion122B as a “second recess”, and the recess 137 in the third portion 122Cas a “third recess”. Similarly to the first and second recesses 137, thethird recess 139 may or may not reach the root of the waveguide member122.

FIG. 27 is a perspective view showing enlarged only a portion of thewaveguide member 122 for ease of understanding. As shown in the figure,in the present example embodiment, the height of the waveguide surface122 a at the impedance transformer 138A is greater than the height ofthe waveguide surface 122 a at the second portion 122B and third portion122C. Therefore, capacitive coupling occurs between the side surface 138a of the impedance transformer 138A and the conductive surface 110 a ofthe conductive member 110, whereby an unwanted capacitance component C2occurs in the waveguide (see FIG. 11). In the present exampleembodiment, providing the third recess 139 reduces this unwantedcapacitance component C2. Note that the impedance transformers 138A and138B may be provided on the conductive member 110 facing the waveguidesurface 122 a, or provided both on the waveguide surface 122 a and onthe conductive member 110. Such examples will be described later withreference to FIG. 29A and FIG. 29B.

FIG. 28 is a diagram showing an equivalent circuit of the ridgewaveguide according to the present example embodiment. A structurehaving the third recess 139 is equivalent to a structure where aninductance component L2 is added in parallel to the capacitancecomponent C2. By providing the recess 139 in addition to the recess 135and the two recesses 137, not only the capacitance components C1associated with bending at the branching portion 136, but also thecapacitance component C2 associated with the impedance transformer 138Acan be canceled. The magnitude of the added inductance component L2depends on the shape, size, and position of the third recess 139.Therefore, the shape, size, and position of the third recess 139 may bedesigned so that the inductance components L1 and L2 will cancel thecapacitance components C1 and C2.

With such a construction, impedance matching is established at thebranching portion 136 and signal wave reflection can be suppressed,whereby a decrease in transmission efficiency can be reduced.

In the present example embodiment, inductance components can be added tothe branching portion 136 in two ways, thereby making it so much easierto establish matching. In particular, this facilitates matching across abroad frequency band, which will be required in the case of handlingradio waves of the UWB (Ultra Wide Band), for which a license is not arequisite.

Other Example Embodiments

The waveguide device according to the present disclosure permits variousmodifications, without being limited to the above example embodiments.Hereinafter, other example embodiments of the waveguide device will bedescribed.

In Example Embodiments 4 and 5, recesses 137 are made in side surfacesof both of the second portion 122B and the third portion 122C of thewaveguide member 122; alternatively, a recess 137 may be made in a sidesurface of either one of them. Such a construction will particularlyfind its use in the cases where an angle constituted by the directionthat the first portion 122A of the waveguide member 122 extends and thedirection that the second portion 122B extends is different from anangle constituted by the direction that the first portion 122A extendsand the direction that the third portion 122C extends.

FIG. 29A and FIG. 29B are cross-sectional views schematically showingother examples of the impedance transformer 138. In the example shown inFIG. 29A, protrusions function as impedance transformers 138 are formedon the conductive surface 110 a of the conductive member 110. On theother hand, in the example shown in FIG. 29B, structures functioning asimpedance transformers 138 are formed on both of the conductive surface110 a and the waveguide surface 122 a. In the example of FIG. 29B,neither the waveguide member 122 nor the conductive member 110 has astructure with a length of λr/4 per se along the Y direction, but incombination, they define a region with a length of λr/4 with a smallergap than at any adjacent site. In the present disclosure, such astructure also qualifies as an impedance transformer 138. As in theseexamples, the impedance transformer 138 may be formed on at least oneof: the waveguide surface 122 a of the waveguide member 122 at the firstportion 122A; and the conductive surface 110 a opposing the waveguidesurface 122 a. Each impedance transformer 138 spans a length of λr/4along the Y direction from one end of the first portion 122A. In theexamples shown in FIG. 29A and FIG. 29B, each impedance transformer 138is a portion with a smaller gap size between the waveguide surface 122 aand the conductive surface 110 a than in any adjacent site, and includesat least a portion of a protrusion on at least one of the waveguidesurface 122 a and the conductive surface 110 a.

As described earlier, the length of each impedance transformer 138 alongthe Y direction is not limited to λr/4. Under the influence of parasiticcapacitance and the like associated with the WRG, an optimum length ofan impedance transformer 138 may vary from λr/4. The length of eachimpedance transformer 138 along the waveguide surface 122 a may be equalto or greater than the width of the waveguide surface 122 a and lessthan three times the width of the waveguide surface 122 a, for example.Note that the width of the waveguide surface 122 a may vary withposition, as in Example Embodiment 2. In that case, the “width” of thewaveguide surface 122 a means the width of the broadest portion of thewaveguide surface 122 a.

Next, with reference to FIGS. 30A through 30D, other exemplary gapenlargements according to example embodiments of the present disclosurewill be described.

FIG. 30A shows an example where, as viewed in a direction perpendicularto the conductive surface 110 a, the dimension of a gap enlargement 141along the width direction of the first portion 122A of the waveguidemember decreases toward the first portion 122A. In this example, as seenthrough in a direction perpendicular to any site on the conductivesurface that is around the gap enlargement 141, the outer edge of thegap enlargement reaches an edge 143 of the two branches 122B and 122C orthe junction on the opposite side from the first portion 122A, but doesnot reach two edges 145 of the first portion 122A.

FIG. 30B shows an example where, as viewed in a direction perpendicularto the conductive surface 110 a, the dimension of a gap enlargement 141along the width direction of the first portion 122A of the waveguidemember increases toward the first portion 122A. In this example, as seenthrough in a direction perpendicular to any site on the conductivesurface that is around the gap enlargement 141, the outer edge of thegap enlargement reaches an edge 143 of the two branches 122B and 122C orthe junction on the opposite side from the first portion 122A, and alsoreaches two edges 145 of the first portion 122A.

In the examples shown in FIG. 30A and FIG. 30B, the shape of the gapenlargement as viewed in a direction perpendicular to the conductivesurface 110 a is a trapezoid, rather than a rectangle.

FIG. 30C shows an example where a gap enlargement 141 of an ellipticshape is provided in a central portion of a branching portion of thewaveguide member, without reaching the edge of any of the first portion122A, the second portion 122B, or the third portion 122C. FIG. 30D showsan example where a gap enlargement 141 of a semicircular shape islocated adjacent to an end of the first portion 122A of the waveguidemember. In these constructions, too, effects of the example embodimentsof the present disclosure can be obtained.

The side walls of junction between the first portion and each branch ofthe waveguide member may be rounded. In other words, the side-surfacejunction between the side surface of the first portion and the sidesurface(s) of at least one of the second and third portions of thewaveguide member may be curved. For example, as shown in FIG. 31A, theside surface of the first portion 122A and the side surfaces of thesecond portion 122B and the third portion 122C may present curvedconnection. Furthermore, as shown in FIG. 31B, the side surface of thefourth portion 122D and the side surfaces of the second portion 122B andthe third portion 122C may also present curved connection.

Thus, a waveguide device according to an example embodiment of thepresent disclosure includes: a conductive member 110 having a conductivesurface 110 a; a waveguide member 122 having an electrically-conductivewaveguide surface 122 a which is opposed to the conductive surface 110 aand an electrically-conductive side surface which is connected to thewaveguide surface 122 a, and extending alongside the conductive surface110 a; and an artificial magnetic conductor extending on both sides ofthe waveguide member 122. The waveguide member 122 includes: a firstportion 122A extending in one direction; and at least two branchesextending from one end of the first portion 122A, the at least twobranches including a second portion 122B and a third portion 122C thatextend in mutually different directions. A waveguide which is defined bythe conductive surface 110 a, the waveguide surface 122 a, and theartificial magnetic conductor includes a gap enlargement at which a gapbetween the conductive surface 110 a and the waveguide surface 122 a islocally enlarged. At least a part of a junction at which the firstportion 122A of the waveguide member 122 becomes jointed with the atleast two branches overlaps the gap enlargement, as seen through in adirection perpendicular to the conductive surface 110 a. With suchconstruction, the degree of impedance matching at any branching portioncan be enhanced.

<Antenna Device>

Next, an illustrative example embodiment of an antenna device includingthe waveguide device according to the present disclosure will bedescribed.

An antenna device according to the present example embodiment includes awaveguide device according to any of the above example embodiments andat least one antenna element connected to the waveguide device. Theantenna element has at least one of the function of radiating into spacean electromagnetic wave which has propagated through a waveguide in thewaveguide device and the function of allowing an electromagnetic wavewhich has propagated in space to be introduced into a waveguide in thewaveguide device. In other words, the antenna device according to thepresent example embodiment is used for at least one of transmission andreception of signals.

FIG. 32A is an upper plan view of an antenna device (array antenna)including 16 slots (openings) 112 in an array of 4 rows and 4 columns,as viewed from the Z direction. FIG. 32B is a cross-sectional view takenalong line B-B in FIG. 32A. In the antenna device shown in the figures,a first waveguide device 100 a and a second waveguide device 100 b arelayered. The first waveguide device 100 a includes waveguide members122U that directly couple to slots 112 functioning as radiation elements(antenna elements). The second waveguide device 100 b includes furtherwaveguide members 122L that couple to the waveguide members 122U of thefirst waveguide device 100 a. The waveguide members 122L and theconductive rods 124L of the second waveguide device 100 b are arrangedon a third conductive member 140. The second waveguide device 100 b isbasically similar in construction to the first waveguide device 100 a.

On the first conductive member 110 in the first waveguide device 100 a,side walls 114 surrounding each slot 112 are provided. The side walls114 form a horn that adjusts directivity of the slot 112. The number andarrangement of slots 112 in this example are only illustrative. Theorientations and shapes of the slots 112 are not limited to those of theexample shown in the figures, either. It is not intended that theexample shown in the figures provides any limitation as to whether theside walls 114 of each horn are tilted or not, the angles thereof, orthe shape of each horn.

FIG. 33A is a diagram showing a planar layout of waveguide members 122Uin the first waveguide device 100 a. FIG. 33B is a diagram showing aplanar layout of a waveguide member 122L in the second waveguide device100 b. As is clear from these figures, the waveguide members 122U of thefirst waveguide device 100 a extend linearly, and include no branchingportions or bends. On the other hand, the waveguide members 122L of thesecond waveguide device 100 b include both branching portions and bends.In terms of fundamental construction of the waveguide device, thecombination of the “second conductive member 120” and the “thirdconductive member 140” in the second waveguide device 100 b correspondsto the combination in the first waveguide device 100 a of the “firstconductive member 110” and the “second conductive member 120”.

What is characteristic in the array antenna shown in the figures is thatrecesses 135 are respectively formed in three branching portions 136 ofthe waveguide member 122L. As a result, the degree of impedance matchingis improved at the branching portions 136 of the waveguide members 122L.

The waveguide members 122U of the first waveguide device 100 a couple tothe waveguide member 122L of the second waveguide device 100 b, throughports (openings) 145U that are provided in the second conductive member120. Stated otherwise, an electromagnetic wave which has propagatedthrough the waveguide member 122L of the second waveguide device 100 bpasses through a port 145U to reach a waveguide member 122U of the firstwaveguide device 100 a, and propagates through the waveguide member 122Uof the first waveguide device 100 a. In this case, each slot 112functions as an antenna element to allow an electromagnetic wave whichhas propagated through the waveguide to be emitted into space.Conversely, when an electromagnetic wave which has propagated in spaceimpinges on a slot 112, the electromagnetic wave couples to thewaveguide member 122U of the first waveguide device 100 a that liesdirectly under that slot 112, and propagates through the waveguidemember 122U of the first waveguide device 100 a. An electromagnetic wavewhich has propagated through a waveguide member 122U of the firstwaveguide device 100 a may also pass through a port 145U to reach thewaveguide member 122L of the second waveguide device 100 b, andpropagates through the waveguide member 122L of the second waveguidedevice 100 b. Via a port 145L of the third conductive member 140, thewaveguide member 122L of the second waveguide device 100 b may couple toan external waveguide device or radio frequency circuit (electroniccircuit).

As one example, FIG. 33B illustrates an electronic circuit 200 which isconnected to the port 145L. Without being limited to a specificposition, the electronic circuit 200 may be provided at any arbitraryposition. The electronic circuit 200 may be provided on a circuit boardwhich is on the rear surface side (i.e., the lower side in FIG. 32B) ofthe third conductive member 140, for example. Such an electronic circuitis a microwave integrated circuit, which may be an MMIC (MonolithicMicrowave Integrated Circuit) that generates or receives millimeterwaves, for example.

The first conductive member 110 shown in FIG. 32A may be called an“emission layer”. Moreover, the entirety of the second conductive member120, the waveguide members 122U, and the conductive rods 124U shown inFIG. 33A may be called an “excitation layer”, whereas the entirety ofthe third conductive member 140, the waveguide member 122L, and theconductive rods 124L shown in FIG. 33B may be called a “distributionlayer”. Moreover, the “excitation layer” and the “distribution layer”may be collectively called a “feeding layer”. Each of the “emissionlayer”, the “excitation layer”, and the “distribution layer” can bemass-produced by processing a single metal plate. The radiation layer,the excitation layer, the distribution layer, and the electroniccircuitry to be provided on the rear face side of the distribution layermay be fabricated as a single-module product.

In the array antenna of this example, as can be seen from FIG. 32B, anemission layer, an excitation layer, and a distribution layer arelayered, which are in plate form; therefore, a flat and low-profile flatpanel antenna is realized as a whole. For example, the height(thickness) of a multilayer structure having a cross-sectionalconstruction as shown in FIG. 32B can be set to 10 mm or less.

With the waveguide member 122L shown in FIG. 33B, the distances from theport 145L of the third conductive member 140 to the respective ports145U (see FIG. 33A) of the second conductive member 120 measured alongthe waveguide member 122L are all equal. Therefore, a signal wave whichis input to the waveguide member 122L reaches the four ports 145U of thesecond conductive member 120 all in the same phase, from the port 145Lof the third conductive member 140. As a result, the four waveguidemembers 122U on the second conductive member 120 can be excited in thesame phase.

It is not necessary for all slots 112 functioning as antenna elements toemit electromagnetic waves in the same phase. The network patterns ofthe waveguide members 122U and 122L in the excitation layer and thedistribution layer may be arbitrary, and they may be arranged so thatthe respective waveguide members 122U and 122L independently propagatedifferent signals.

Although the waveguide members 122U of the first waveguide device 100 ain this example include neither a branching portion nor a bend, thewaveguide device functioning as an excitation layer may also include awaveguide member having at least one of a branching portion and a bend.In the example shown in FIG. 33A, each port 145U is located at thecentral portion of the waveguide member 122U. By placing the port 145Uat the central portion of the waveguide member 122U, the distance fromthe port 145U to the slot 112 located at the end of the waveguide member122U can be shortened. Shortening this distance will reduce the phasedifferences at each slot 112 to occur when the frequency of theelectromagnetic wave is varied, thereby making it possible to excite theslots 112 under appropriate phase conditions over a broader band.

<Other Variants>

Next, variants of waveguide structures including the waveguide member122, the conductive members 110 and 120, and the plurality of conductiverods 124 will be described. The following variants are applicable to theWRG structure in any place in each of the example embodiments describedabove.

FIG. 34A is a cross-sectional view showing an exemplary structure inwhich only the waveguide surface 122 a, defining an upper face of thewaveguide member 122, is electrically conductive, while any portion ofthe waveguide member 122 other than the waveguide surface 122 a is notelectrically conductive. Both of the conductive member 110 and theconductive member 120 alike are only electrically conductive at theirsurface that has the waveguide member 122 provided thereon (i.e., theconductive surface 110 a, 120 a), while not being electricallyconductive in any other portions. Thus, each of the waveguide member122, the conductive member 110, and the conductive member 120 does notneed to be electrically conductive.

FIG. 34B is a diagram showing a variant in which the waveguide member122 is not formed on the conductive member 120. In this example, thewaveguide member 122 is fixed to a supporting member (e.g., the innerwall of the housing) that supports the conductive member 110 and theconductive member. A gap exists between the waveguide member 122 and theconductive member 120. Thus, the waveguide member 122 does not need tobe connected to the conductive member 120.

FIG. 34C is a diagram showing an exemplary structure where theconductive member 120, the waveguide member 122, and each of theplurality of conductive rods 124 are composed of a dielectric surfacethat is coated with an electrically conductive material such as a metal.The conductive member 120, the waveguide member 122, and the pluralityof conductive rods 124 are connected to one another via the electricalconductor. On the other hand, the conductive member 110 is made of anelectrically conductive material such as a metal.

FIG. 34D and FIG. 34E are diagrams each showing an exemplary structurein which dielectric layers 110 c and 120 c are respectively provided onthe outermost surfaces of conductive members 110 and 120, a waveguidemember 122, and conductive rods 124. FIG. 34D shows an exemplarystructure in which the surface of metal conductive members, which areelectrical conductors, are covered with a dielectric layer. FIG. 34Eshows an example where the conductive member 120 is structured so thatthe surface of members which are composed of a dielectric, e.g., resin,is covered with an electrical conductor such as a metal, this metallayer being further coated with a dielectric layer. The dielectric layerthat covers the metal surface may be a coating of resin or the like, oran oxide film of passivation coating or the like which is generated asthe metal becomes oxidized.

The dielectric layer on the outermost surface will allow losses to beincreased in the electromagnetic wave propagating through the WRGwaveguide, but is able to protect the conductive surfaces 110 a and 120a (which are electrically conductive) from corrosion. It also preventsinfluences of a DC voltage, or an AC voltage of such a low frequencythat it is not capable of propagation on certain WRG waveguides.

FIG. 34F is a diagram showing an example where the height of thewaveguide member 122 is lower than the height of the conductive rods124, and the portion of the conductive surface 110 a of the conductivemember 110 that opposes the waveguide surface 122 a protrudes toward thewaveguide member 122. Even such a structure will operate in a similarmanner to the above-described example embodiment, so long as the rangesof dimensions depicted in FIG. 4 are satisfied.

FIG. 34G is a diagram showing an example where, further in the structureof FIG. 34F, portions of the conductive surface 110 a that oppose theconductive rods 124 protrude toward the conductive rods 124. Even such astructure will operate in a similar manner to the above-describedexample embodiment, so long as the ranges of dimensions depicted in FIG.4 are satisfied. Instead of a structure in which the conductive surface110 a partially protrudes, a structure in which the conductive surface110 a is partially dented may be adopted.

FIG. 35A is a diagram showing an example where a conductive surface 110a of the conductive member 110 is shaped as a curved surface. FIG. 35Bis a diagram showing an example where also a conductive surface 120 a ofthe conductive member 120 is shaped as a curved surface. As demonstratedby these examples, the conductive surfaces 110 a and 120 a may not beshaped as planes, but may be shaped as curved surfaces. A conductivemember having a conductive surface which is a curved surface is alsoqualifies as a conductive member having a “plate shape”.

In the waveguide device 100 of the above-described construction, asignal wave of the operating frequency is unable to propagate in thespace between the surface 125 of the artificial magnetic conductor andthe conductive surface 110 a of the conductive member 110, butpropagates in the space between the waveguide surface 122 a of thewaveguide member 122 and the conductive surface 110 a of the conductivemember 110. Unlike in a hollow waveguide, the width of the waveguidemember 122 in such a waveguide structure does not need to be equal to orgreater than a half of the wavelength of the electromagnetic wave topropagate. Moreover, the conductive member 110 and the conductive member120 do not need to be electrically interconnected by a metal wall thatextends along the thickness direction (i.e., in parallel to the YZplane).

An antenna device (slot array antenna) according to an exampleembodiment of the present disclosure can be suitably used in a radardevice or a radar system to be incorporated in moving entities such asvehicles, marine vessels, aircraft, robots, or the like, for example. Aradar device would include a slot array antenna according to an exampleembodiment of the present disclosure and a microwave integrated circuitthat is connected to the slot array antenna. A radar system wouldinclude the radar device and a signal processing circuit that isconnected to the microwave integrated circuit of the radar device. Anantenna device according to an example embodiment of the presentdisclosure includes a multi-layered WRG structure which permitsdownsizing, and thus allows the area of the face on which antennaelements are arrayed to be significantly reduced, as compared to aconstruction in which a conventional hollow waveguide is used.Therefore, a radar system incorporating the antenna device can be easilymounted in a narrow place such as a face of a rearview mirror in avehicle that is opposite to its specular surface, or a small-sizedmoving entity such as a UAV (an Unmanned Aerial Vehicle, a so-calleddrone). Note that, without being limited to the implementation where itis mounted in a vehicle, a radar system may be used while being fixed onthe road or a building, for example.

A slot array antenna according to an example embodiment of the presentdisclosure can also be used in a wireless communication system. Such awireless communication system would include a slot array antennaaccording to any of the above example embodiments and a communicationcircuit (a transmission circuit or a reception circuit). Details ofexemplary applications to wireless communication systems will bedescribed later.

A slot array antenna according to an example embodiment of the presentdisclosure can further be used as an antenna in an indoor positioningsystem (IPS). An indoor positioning system is able to identify theposition of a moving entity, such as a person or an automated guidedvehicle (AGV), that is in a building. A slot array antenna can also beused as a radio wave transmitter (beacon) for use in a system whichprovides information to an information terminal device (e.g., asmartphone) that is carried by a person who has visited a store or anyother facility. In such a system, once every several seconds, a beaconmay radiate an electromagnetic wave carrying an ID or other informationsuperposed thereon, for example. When the information terminal devicereceives this electromagnetic wave, the information terminal devicetransmits the received information to a remote server computer viatelecommunication lines. Based on the information that has been receivedfrom the information terminal device, the server computer identifies theposition of that information terminal device, and provides informationwhich is associated with that position (e.g., product information or acoupon) to the information terminal device.

The present specification employs the term “artificial magneticconductor” in describing the technique according to the presentdisclosure, this being in line with what is set forth in a paper by oneof the inventors Kirino (H. Kirino and K. Ogawa, “A 76 GHz Multi-LayeredPhased Array Antenna using a Non-Metal Contact Metamaterial Wavegude”,IEEE Transaction on Antenna and Propagation, Vol. 60, No. 2, pp.840-853, February, 2012) as well as a paper by Kildal et al., whopublished a study directed to related subject matter around the sametime. However, it has been found through a study by the inventors thatthe invention according to the present disclosure does not necessarilyrequire an “artificial magnetic conductor” under its conventionaldefinition. That is, while a periodic structure has been believed to bea requirement for an artificial magnetic conductor, the inventionaccording to the present disclosure does not necessary require aperiodic structure in order to be practiced.

The artificial magnetic conductor that is described in the presentdisclosure consists of rows of conductive rods. Therefore, in order toprevent electromagnetic waves from leaking away from the waveguidesurface, it has been believed essential that there exist at least tworows of conductive rods on one side of the waveguide member(s), suchrows of conductive rods extending along the waveguide member(s)(ridge(s)). The reason is that it takes at least two rows of conductiverods for them to have a “period”. However, according to a study by theinventors, even when only one row of conductive rods exists between twowaveguide members that extend in parallel to each other, the intensityof a signal that leaks from one waveguide member to the other waveguidemember can be suppressed to −10 dB or less, which is a practicallysufficient value in many applications. The reason why such a sufficientlevel of separation is achieved with only an imperfect periodicstructure is so far unclear. However, in view of this fact, in thepresent disclosure, the notion of “artificial magnetic conductor” isextended so that the term also encompasses a structure including onlyone row of conductive rods.

Application Example 1: Onboard Radar System

Next, as an Application Example of utilizing the above-described slotarray antenna, an instance of an onboard radar system including a slotarray antenna will be described. A transmission wave used in an onboardradar system may have a frequency of e.g. 76 gigahertz (GHz) band, whichwill have a wavelength λo of about 4 mm in free space.

In safety technology of automobiles, e.g., collision avoidance systemsor automated driving, it is particularly essential to identify one ormore vehicles (targets) that are traveling ahead of the driver'svehicle. As a method of identifying vehicles, techniques of estimatingthe directions of arriving waves by using a radar system have been underdevelopment.

FIG. 36 shows a driver's vehicle 500, and a preceding vehicle 502 thatis traveling in the same lane as the driver's vehicle 500. The driver'svehicle 500 includes an onboard radar system which incorporates a slotarray antenna according to any of the above-described exampleembodiments. When the onboard radar system of the driver's vehicle 500radiates a radio frequency transmission signal, the transmission signalreaches the preceding vehicle 502 and is reflected therefrom, so that apart of the signal returns to the driver's vehicle 500. The onboardradar system receives this signal to calculate a position of thepreceding vehicle 502, a distance (“range”) to the preceding vehicle502, velocity, etc.

FIG. 37 shows the onboard radar system 510 of the driver's vehicle 500.The onboard radar system 510 is provided within the vehicle. Morespecifically, the onboard radar system 510 is disposed on a face of therearview mirror that is opposite to its specular surface. From withinthe vehicle, the onboard radar system 510 radiates a radio frequencytransmission signal in the direction of travel of the vehicle 500, andreceives a signal(s) which arrives from the direction of travel.

The onboard radar system 510 of this Application Example includes a slotarray antenna according to an example embodiment of the presentdisclosure. The slot array antenna may include a plurality of waveguidemembers that are parallel to one another. They are to be arranged sothat the plurality of waveguide members each extend in a direction whichcoincides with the vertical direction, and that the plurality ofwaveguide members are arranged in a direction which coincides with thehorizontal direction. As a result, the lateral and vertical dimensionsof the plurality of slots as viewed from the front can be furtherreduced.

Exemplary dimensions of an antenna device including the above arrayantenna may be 60 mm (wide)×30 mm (long)×10 mm (deep). It will beappreciated that this is a very small size for a millimeter wave radarsystem of the 76 GHz band.

Note that many a conventional onboard radar system is provided outsidethe vehicle, e.g., at the tip of the front nose. The reason is that theonboard radar system is relatively large in size, and thus is difficultto be provided within the vehicle as in the present disclosure. Theonboard radar system 510 of this Application Example may be installedwithin the vehicle as described above, but may instead be mounted at thetip of the front nose. Since the footprint of the onboard radar systemon the front nose is reduced, other parts can be more easily placed.

The Application Example allows the interval between a plurality ofwaveguide members (ridges) that are used in the transmission antenna tobe narrow, which also narrows the interval between a plurality of slotsto be provided opposite from a number of adjacent waveguide members.This reduces the influences of grating lobes. For example, when theinterval between the centers of two laterally adjacent slots is shorterthan the free-space wavelength λo of the transmission wave (i.e., lessthan about 4 mm), no grating lobes will occur frontward. As a result,influences of grating lobes are reduced. Note that grating lobes willoccur when the interval at which the antenna elements are arrayed isgreater than a half of the wavelength of an electromagnetic wave. If theinterval at which the antenna elements are arrayed is less than thewavelength, no grating lobes will occur frontward. Therefore, in thecase where no beam steering is performed to impart phase differencesamong the radio waves radiated from the respective antenna elementscomposing an array antenna, grating lobes will exert substantially noinfluences so long as the interval at which the antenna elements arearrayed is smaller than the wavelength. By adjusting the array factor ofthe transmission antenna, the directivity of the transmission antennacan be adjusted. A phase shifter may be provided so as to be able toindividually adjust the phases of electromagnetic waves that aretransmitted on plural waveguide members. In that case, even if theinterval between antenna elements is made less than the free-spacewavelength λo of the transmission wave, grating lobes will appear as thephase shift amount is increased. However, when the intervals between theantenna elements is reduced to less than a half of the free spacewavelength λo of the transmission wave, grating lobes will not appearirrespective of the phase shift amount. By providing a phase shifter,the directivity of the transmission antenna can be changed in anydesired direction. Since the construction of a phase shifter iswell-known, description thereof will be omitted.

A reception antenna according to the Application Example is able toreduce reception of reflected waves associated with grating lobes,thereby being able to improve the precision of the below-describedprocessing. Hereinafter, an example of a reception process will bedescribed.

FIG. 38A shows a relationship between an array antenna AA of the onboardradar system 510 and plural arriving waves k (k: an integer from 1 to K;the same will always apply below. K is the number of targets that arepresent in different azimuths). The array antenna AA includes M antennaelements in a linear array. Principlewise, an antenna can be used forboth transmission and reception, and therefore the array antenna AA canbe used for both a transmission antenna and a reception antenna.Hereinafter, an example method of processing an arriving wave which isreceived by the reception antenna will be described.

The array antenna AA receives plural arriving waves that simultaneouslyimpinge at various angles. Some of the plural arriving waves may bearriving waves which have been radiated from the transmission antenna ofthe same onboard radar system 510 and reflected by a target(s).Furthermore, some of the plural arriving waves may be direct or indirectarriving waves that have been radiated from other vehicles.

The incident angle of each arriving wave (i.e., an angle representingits direction of arrival) is an angle with respect to the broadside B ofthe array antenna AA. The incident angle of an arriving wave representsan angle with respect to a direction which is perpendicular to thedirection of the line along which antenna elements are arrayed.

Now, consider a k^(th) arriving wave. Where K arriving waves areimpinging on the array antenna from K targets existing at differentazimuths, a “k^(th) arriving wave” means an arriving wave which isidentified by an incident angle θ_(k).

FIG. 38B shows the array antenna AA receiving the k^(th) arriving wave.The signals received by the array antenna AA can be expressed as a“vector” having M elements, by Math. 1.

S=[s ₁ ,s ₂ , . . . ,s _(M)]^(T)  [Math. 1]

In the above, s_(m) (where m is an integer from 1 to M; the same willalso be true hereinbelow) is the value of a signal which is received byan m^(th) antenna element. The superscript ^(T) means transposition. Sis a column vector. The column vector S is defined by a product ofmultiplication between a direction vector (referred to as a steeringvector or a mode vector) as determined by the construction of the arrayantenna and a complex vector representing a signal from each target(also referred to as a wave source or a signal source). When the numberof wave sources is K, the waves of signals arriving at each individualantenna element from the respective K wave sources are linearlysuperposed. In this state, s_(m) can be expressed by Math. 2.

$\begin{matrix}{s_{m} = {\sum\limits_{k = 1}^{K}{a_{k}\exp \left\{ {j\left( {{\frac{{2\pi}\;}{\lambda}d_{m}\sin \; \theta_{k}} + \phi_{k}} \right)} \right\}}}} & \left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Math. 2, a_(k), θ_(k) and φ_(k) respectively denote the amplitude,incident angle, and initial phase of the k^(th) arriving wave. Moreover,λ denotes the wavelength of an arriving wave, and j is an imaginaryunit.

As will be understood from Math. 2, s_(m) is expressed as a complexnumber consisting of a real part (Re) and an imaginary part (Im).

When this is further generalized by taking noise (internal noise orthermal noise) into consideration, the array reception signal X can beexpressed as Math. 3.

X=S+N  [Math. 3]

N is a vector expression of noise.

The signal processing circuit generates a spatial covariance matrix Rxx(Math. 4) of arriving waves by using the array reception signal Xexpressed by Math. 3, and further determines eigenvalues of the spatialcovariance matrix Rxx.

$\begin{matrix}\begin{matrix}{R_{xx} = {XX}^{H}} \\{= \begin{bmatrix}{Rxx}_{11} & \ldots & {Rxx}_{1M} \\\vdots & \ddots & \vdots \\{Rxx}_{M\; 1} & \ldots & {Rxx}_{MM}\end{bmatrix}}\end{matrix} & \left\lbrack {{Math}.\mspace{14mu} 4} \right\rbrack\end{matrix}$

In the above, the superscript H means complex conjugate transposition(Hermitian conjugate).

Among the eigenvalues, the number of eigenvalues which have values equalto or greater than a predetermined value that is defined based onthermal noise (signal space eigenvalues) corresponds to the number ofarriving waves. Then, angles that produce the highest likelihood as tothe directions of arrival of reflected waves (i.e. maximum likelihood)are calculated, whereby the number of targets and the angles at whichthe respective targets are present can be identified. This process isknown as a maximum likelihood estimation technique.

Next, see FIG. 39. FIG. 39 is a block diagram showing an exemplaryfundamental construction of a vehicle travel controlling apparatus 600according to the present disclosure. The vehicle travel controllingapparatus 600 shown in FIG. 39 includes a radar system 510 which ismounted in a vehicle, and a travel assistance electronic controlapparatus 520 which is connected to the radar system 510. The radarsystem 510 includes an array antenna AA and a radar signal processingapparatus 530.

The array antenna AA includes a plurality of antenna elements, each ofwhich outputs a reception signal in response to one or plural arrivingwaves. As mentioned earlier, the array antenna AA is capable ofradiating a millimeter wave of a high frequency.

In the radar system 510, the array antenna AA needs to be attached tothe vehicle, while at least some of the functions of the radar signalprocessing apparatus 530 may be implemented by a computer 550 and adatabase 552 which are provided externally to the vehicle travelcontrolling apparatus 600 (e.g., outside of the driver's vehicle). Inthat case, the portions of the radar signal processing apparatus 530that are located within the vehicle may be perpetually or occasionallyconnected to the computer 550 and database 552 external to the vehicleso that bidirectional communications of signal or data are possible. Thecommunications are to be performed via a communication device 540 of thevehicle and a commonly-available communications network.

The database 552 may store a program which defines various signalprocessing algorithms. The content of the data and program needed forthe operation of the radar system 510 may be externally updated via thecommunication device 540. Thus, at least some of the functions of theradar system 510 can be realized externally to the driver's vehicle(which is inclusive of the interior of another vehicle), by a cloudcomputing technique. Therefore, an “onboard” radar system in the meaningof the present disclosure does not require that all of its constituentelements be mounted within the (driver's) vehicle. However, forsimplicity, the present application will describe an implementation inwhich all constituent elements according to the present disclosure aremounted in a single vehicle (i.e., the driver's vehicle), unlessotherwise specified.

The radar signal processing apparatus 530 includes a signal processingcircuit 560. The signal processing circuit 560 directly or indirectlyreceives reception signals from the array antenna AA, and inputs thereception signals, or a secondary signal(s) which has been generatedfrom the reception signals, to an arriving wave estimation unit AU. Apart or a whole of the circuit (not shown) which generates a secondarysignal(s) from the reception signals does not need to be provided insideof the signal processing circuit 560. A part or a whole of such acircuit (preprocessing circuit) may be provided between the arrayantenna AA and the radar signal processing apparatus 530.

The signal processing circuit 560 is configured to perform computationby using the reception signals or secondary signal(s), and output asignal indicating the number of arriving waves. As used herein, a“signal indicating the number of arriving waves” can be said to be asignal indicating the number of preceding vehicles (which may be onepreceding vehicle or plural preceding vehicles) ahead of the driver'svehicle.

The signal processing circuit 560 may be configured to execute varioussignal processing which is executable by known radar signal processingapparatuses. For example, the signal processing circuit 560 may beconfigured to execute “super-resolution algorithms” such as the MUSICmethod, the ESPRIT method, or the SAGE method, or other algorithms fordirection-of-arrival estimation of relatively low resolution.

The arriving wave estimation unit AU shown in FIG. 39 estimates an anglerepresenting the azimuth of each arriving wave by an arbitrary algorithmfor direction-of-arrival estimation, and outputs a signal indicating theestimation result. The signal processing circuit 560 estimates thedistance to each target as a wave source of an arriving wave, therelative velocity of the target, and the azimuth of the target by usinga known algorithm which is executed by the arriving wave estimation unitAU, and output a signal indicating the estimation result.

In the present disclosure, the term “signal processing circuit” is notlimited to a single circuit, but encompasses any implementation in whicha combination of plural circuits is conceptually regarded as a singlefunctional part. The signal processing circuit 560 may be realized byone or more System-on-Chips (SoCs). For example, a part or a whole ofthe signal processing circuit 560 may be an FPGA (Field-ProgrammableGate Array), which is a programmable logic device (PLD). In that case,the signal processing circuit 560 includes a plurality of computationelements (e.g., general-purpose logics and multipliers) and a pluralityof memory elements (e.g., look-up tables or memory blocks).Alternatively, the signal processing circuit 560 may be a set of ageneral-purpose processor(s) and a main memory device(s). The signalprocessing circuit 560 may be a circuit which includes a processorcore(s) and a memory device(s). These may function as the signalprocessing circuit 560.

The travel assistance electronic control apparatus 520 is configured toprovide travel assistance for the vehicle based on various signals whichare output from the radar signal processing apparatus 530. The travelassistance electronic control apparatus 520 instructs various electroniccontrol units to fulfill predetermined functions, e.g., a function ofissuing an alarm to prompt the driver to make a braking operation whenthe distance to a preceding vehicle (vehicular gap) has become shorterthan a predefined value; a function of controlling the brakes; and afunction of controlling the accelerator. For example, in the case of anoperation mode which performs adaptive cruise control of the driver'svehicle, the travel assistance electronic control apparatus 520 sendspredetermined signals to various electronic control units (not shown)and actuators, to maintain the distance of the driver's vehicle to apreceding vehicle at a predefined value, or maintain the travelingvelocity of the driver's vehicle at a predefined value.

In the case of the MUSIC method, the signal processing circuit 560determines eigenvalues of the spatial covariance matrix, and, as asignal indicating the number of arriving waves, outputs a signalindicating the number of those eigenvalues (“signal space eigenvalues”)which are greater than a predetermined value (thermal noise power) thatis defined based on thermal noise.

Next, see FIG. 40. FIG. 40 is a block diagram showing another exemplaryconstruction for the vehicle travel controlling apparatus 600. The radarsystem 510 in the vehicle travel controlling apparatus 600 of FIG. 40includes an array antenna AA, which includes an array antenna that isdedicated to reception only (also referred to as a reception antenna) Rxand an array antenna that is dedicated to transmission only (alsoreferred to as a transmission antenna) Tx; and an object detectionapparatus 570.

At least one of the transmission antenna Tx and the reception antenna Rxhas the aforementioned waveguide structure. The transmission antenna Txradiates a transmission wave, which may be a millimeter wave, forexample. The reception antenna Rx that is dedicated to reception onlyoutputs a reception signal in response to one or plural arriving waves(e.g., a millimeter wave(s)).

A transmission/reception circuit 580 sends a transmission signal for atransmission wave to the transmission antenna Tx, and performs“preprocessing” for reception signals of reception waves received at thereception antenna Rx. A part or a whole of the preprocessing may beperformed by the signal processing circuit 560 in the radar signalprocessing apparatus 530. A typical example of preprocessing to beperformed by the transmission/reception circuit 580 may be generating abeat signal from a reception signal, and converting a reception signalof analog format into a reception signal of digital format. In thepresent specification, a device that includes a transmission antenna, areception antenna, a transmission/reception circuit, and a waveguidedevice that allows an electromagnetic wave to propagate between thetransmission antenna and reception antenna and thetransmission/reception circuit is referred to as “radar device”. Asystem that includes an object detection apparatus (including a signalprocessing circuit) in addition to the radar device is referred to as aradar system”.

Note that the radar system according to the present disclosure may,without being limited to the implementation where it is mounted in thedriver's vehicle, be used while being fixed on the road or a building.

Next, an example of a more specific construction of the vehicle travelcontrolling apparatus 600 will be described.

FIG. 41 is a block diagram showing an example of a more specificconstruction of the vehicle travel controlling apparatus 600. Thevehicle travel controlling apparatus 600 shown in FIG. 41 includes aradar system 510 and an onboard camera system 700. The radar system 510includes an array antenna AA, a transmission/reception circuit 580 whichis connected to the array antenna AA, and a signal processing circuit560.

The onboard camera system 700 includes an onboard camera 710 which ismounted in a vehicle, and an image processing circuit 720 whichprocesses an image or video that is acquired by the onboard camera 710.

The vehicle travel controlling apparatus 600 of this Application Exampleincludes an object detection apparatus 570 which is connected to thearray antenna AA and the onboard camera 710, and a travel assistanceelectronic control apparatus 520 which is connected to the objectdetection apparatus 570. The object detection apparatus 570 includes atransmission/reception circuit 580 and an image processing circuit 720,in addition to the above-described radar signal processing apparatus 530(including the signal processing circuit 560). The object detectionapparatus 570 detects a target on the road or near the road, by usingnot only the information which is obtained by the radar system 510 butalso the information which is obtained by the image processing circuit720. For example, while the driver's vehicle is traveling in one of twoor more lanes of the same direction, the image processing circuit 720can distinguish which lane the driver's vehicle is traveling in, andsupply that result of distinction to the signal processing circuit 560.When the number and azimuth(s) of preceding vehicles are to berecognized by using a predetermined algorithm for direction-of-arrivalestimation (e.g., the MUSIC method), the signal processing circuit 560is able to provide more reliable information concerning a spatialdistribution of preceding vehicles by referring to the information fromthe image processing circuit 720.

Note that the onboard camera system 700 is an example of a means foridentifying which lane the driver's vehicle is traveling in. The laneposition of the driver's vehicle may be identified by any other means.For example, by utilizing an ultra-wide band (UWB) technique, it ispossible to identify which one of a plurality of lanes the driver'svehicle is traveling in. It is widely known that the ultra-wide bandtechnique is applicable to position measurement and/or radar. Using theultra-wide band technique enhances the range resolution of the radar, sothat, even when a large number of vehicles exist ahead, each individualtarget can be detected with distinction, based on differences indistance. This makes it possible to accurately identify distance from aguardrail on the road shoulder, or from the median strip. The width ofeach lane is predefined based on each country's law or the like. Byusing such information, it becomes possible to identify where the lanein which the driver's vehicle is currently traveling is. Note that theultra-wide band technique is an example. A radio wave based on any otherwireless technique may be used. Moreover, LIDAR (Light Detection andRanging) may be used together with a radar. LIDAR is sometimes called“laser radar”.

The array antenna AA may be a generic millimeter wave array antenna foronboard use. The transmission antenna Tx in this Application Exampleradiates a millimeter wave as a transmission wave ahead of the vehicle.A portion of the transmission wave is reflected off a target which istypically a preceding vehicle, whereby a reflected wave occurs from thetarget being a wave source. A portion of the reflected wave reaches thearray antenna (reception antenna) AA as an arriving wave. Each of theplurality of antenna elements of the array antenna AA outputs areception signal in response to one or plural arriving waves. In thecase where the number of targets functioning as wave sources ofreflected waves is K (where K is an integer of one or more), the numberof arriving waves is K, but this number K of arriving waves is not knownbeforehand.

The example of FIG. 39 assumes that the radar system 510 is provided asan integral piece, including the array antenna AA, on the rearviewmirror. However, the number and positions of array antennas AA are notlimited to any specific number or specific positions. An array antennaAA may be disposed on the rear surface of the vehicle so as to be ableto detect targets that are behind the vehicle. Moreover, a plurality ofarray antennas AA may be disposed on the front surface and the rearsurface of the vehicle. The array antenna(s) AA may be disposed insidethe vehicle. Even in the case where a horn antenna whose respectiveantenna elements include horns as mentioned above is to be adopted asthe array antenna(s) AA, the array antenna(s) with such antenna elementsmay be situated inside the vehicle.

The signal processing circuit 560 receives and processes the receptionsignals which have been received by the reception antenna Rx andsubjected to preprocessing by the transmission/reception circuit 580.This process encompasses inputting the reception signals to the arrivingwave estimation unit AU, or alternatively, generating a secondarysignal(s) from the reception signals and inputting the secondarysignal(s) to the arriving wave estimation unit AU.

In the example of FIG. 41, a selection circuit 596 which receives thesignal being output from the signal processing circuit 560 and thesignal being output from the image processing circuit 720 is provided inthe object detection apparatus 570. The selection circuit 596 allows oneor both of the signal being output from the signal processing circuit560 and the signal being output from the image processing circuit 720 tobe fed to the travel assistance electronic control apparatus 520.

FIG. 42 is a block diagram showing a more detailed exemplaryconstruction of the radar system 510 according to this ApplicationExample.

As shown in FIG. 42, the array antenna AA includes a transmissionantenna Tx which transmits a millimeter wave and reception antennas Rxwhich receive arriving waves reflected from targets. Although only onetransmission antenna Tx is illustrated in the figure, two or more kindsof transmission antennas with different characteristics may be provided.The array antenna AA includes M antenna elements 11 ₁, 11 ₂, . . . , 11_(M) (where M is an integer of 3 or more). In response to the arrivingwaves, the plurality of antenna elements 11 ₁, 11 ₂, . . . , 11 _(M)respectively output reception signals s₁, s₂, . . . , s_(M) (FIG. 38B).

In the array antenna AA, the antenna elements 11 ₁ to 11 _(M) arearranged in a linear array or a two-dimensional array at fixedintervals, for example. Each arriving wave will impinge on the arrayantenna AA from a direction at an angle θ with respect to the normal ofthe plane in which the antenna elements 11 ₁ to 11 _(M) are arrayed.Thus, the direction of arrival of an arriving wave is defined by thisangle θ.

When an arriving wave from one target impinges on the array antenna AA,this approximates to a plane wave impinging on the antenna elements 11 ₁to 11 _(M) from azimuths of the same angle θ. When K arriving wavesimpinge on the array antenna AA from K targets with different azimuths,the individual arriving waves can be identified in terms of respectivelydifferent angles θ₁ to θ_(K).

As shown in FIG. 42, the object detection apparatus 570 includes thetransmission/reception circuit 580 and the signal processing circuit560.

The transmission/reception circuit 580 includes a triangular wavegeneration circuit 581, a VCO (voltage controlled oscillator) 582, adistributor 583, mixers 584, filters 585, a switch 586, an A/D converter587, and a controller 588. Although the radar system in this ApplicationExample is configured to perform transmission and reception ofmillimeter waves by the FMCW method, the radar system of the presentdisclosure is not limited to this method. The transmission/receptioncircuit 580 is configured to generate a beat signal based on a receptionsignal from the array antenna AA and a transmission signal from thetransmission antenna Tx.

The signal processing circuit 560 includes a distance detection section533, a velocity detection section 534, and an azimuth detection section536. The signal processing circuit 560 is configured to process a signalfrom the A/D converter 587 in the transmission/reception circuit 580,and output signals respectively indicating the detected distance to thetarget, the relative velocity of the target, and the azimuth of thetarget.

First, the construction and operation of the transmission/receptioncircuit 580 will be described in detail.

The triangular wave generation circuit 581 generates a triangular wavesignal, and supplies it to the VCO 582. The VCO 582 outputs atransmission signal having a frequency as modulated based on thetriangular wave signal. FIG. 43 is a diagram showing change in frequencyof a transmission signal which is modulated based on the signal that isgenerated by the triangular wave generation circuit 581. This waveformhas a modulation width Δf and a center frequency of f0. The transmissionsignal having a thus modulated frequency is supplied to the distributor583. The distributor 583 allows the transmission signal obtained fromthe VCO 582 to be distributed among the mixers 584 and the transmissionantenna Tx. Thus, the transmission antenna radiates a millimeter wavehaving a frequency which is modulated in triangular waves, as shown inFIG. 43.

In addition to the transmission signal, FIG. 43 also shows an example ofa reception signal from an arriving wave which is reflected from asingle preceding vehicle. The reception signal is delayed from thetransmission signal. This delay is in proportion to the distance betweenthe driver's vehicle and the preceding vehicle. Moreover, the frequencyof the reception signal increases or decreases in accordance with therelative velocity of the preceding vehicle, due to the Doppler effect.

When the reception signal and the transmission signal are mixed, a beatsignal is generated based on their frequency difference. The frequencyof this beat signal (beat frequency) differs between a period in whichthe transmission signal increases in frequency (ascent) and a period inwhich the transmission signal decreases in frequency (descent). Once abeat frequency for each period is determined, based on such beatfrequencies, the distance to the target and the relative velocity of thetarget are calculated.

FIG. 44 shows a beat frequency fu in an “ascent” period and a beatfrequency fd in a “descent” period. In the graph of FIG. 44, thehorizontal axis represents frequency, and the vertical axis representssignal intensity. This graph is obtained by subjecting the beat signalto time-frequency conversion. Once the beat frequencies fu and fd areobtained, based on a known equation, the distance to the target and therelative velocity of the target are calculated. In this ApplicationExample, with the construction and operation described below, beatfrequencies corresponding to each antenna element of the array antennaAA are obtained, thus enabling estimation of the position information ofa target.

In the example shown in FIG. 42, reception signals from channels Ch₁ toCh_(M) corresponding to the respective antenna elements 11 ₁ to 11 _(M)are each amplified by an amplifier, and input to the correspondingmixers 584. Each mixer 584 mixes the transmission signal into theamplified reception signal. Through this mixing, a beat signal isgenerated corresponding to the frequency difference between thereception signal and the transmission signal. The generated beat signalis fed to the corresponding filter 585. The filters 585 apply bandwidthcontrol to the beat signals on the channels Ch₁ to Ch_(M), and supplybandwidth-controlled beat signals to the switch 586.

The switch 586 performs switching in response to a sampling signal whichis input from the controller 588. The controller 588 may be composed ofa microcomputer, for example. Based on a computer program which isstored in a memory such as a ROM, the controller 588 controls the entiretransmission/reception circuit 580. The controller 588 does not need tobe provided inside the transmission/reception circuit 580, but may beprovided inside the signal processing circuit 560. In other words, thetransmission/reception circuit 580 may operate in accordance with acontrol signal from the signal processing circuit 560. Alternatively,some or all of the functions of the controller 588 may be realized by acentral processing unit which controls the entire transmission/receptioncircuit 580 and signal processing circuit 560.

The beat signals on the channels Ch₁ to Ch_(M) having passed through therespective filters 585 are consecutively supplied to the A/D converter587 via the switch 586. In synchronization with the sampling signal, theA/D converter 587 converts the beat signals on the channels Ch₁ toCh_(M), which are input from the switch 586, into digital signals.

Hereinafter, the construction and operation of the signal processingcircuit 560 will be described in detail. In this Application Example,the distance to the target and the relative velocity of the target areestimated by the FMCW method. Without being limited to the FMCW methodas described below, the radar system can also be implemented by usingother methods, e.g., 2 frequency CW and spread spectrum methods.

In the example shown in FIG. 42, the signal processing circuit 560includes a memory 531, a reception intensity calculation section 532, adistance detection section 533, a velocity detection section 534, a DBF(digital beam forming) processing section 535, an azimuth detectionsection 536, a target link processing section 537, a matrix generationsection 538, a target output processing section 539, and an arrivingwave estimation unit AU. As mentioned earlier, a part or a whole of thesignal processing circuit 560 may be implemented by FPGA, or by a set ofa general-purpose processor(s) and a main memory device(s). The memory531, the reception intensity calculation section 532, the DBF processingsection 535, the distance detection section 533, the velocity detectionsection 534, the azimuth detection section 536, the target linkprocessing section 537, and the arriving wave estimation unit AU may beindividual parts that are implemented in distinct pieces of hardware, orfunctional blocks of a single signal processing circuit.

FIG. 45 shows an exemplary implementation in which the signal processingcircuit 560 is implemented in hardware including a processor PR and amemory device MD. In the signal processing circuit 560 with thisconstruction, too, a computer program that is stored in the memorydevice MD may fulfill the functions of the reception intensitycalculation section 532, the DBF processing section 535, the distancedetection section 533, the velocity detection section 534, the azimuthdetection section 536, the target link processing section 537, thematrix generation section 538, and the arriving wave estimation unit AUshown in FIG. 42.

The signal processing circuit 560 in this Application Example isconfigured to estimate the position information of a preceding vehicleby using each beat signal converted into a digital signal as a secondarysignal of the reception signal, and output a signal indicating theestimation result. Hereinafter, the construction and operation of thesignal processing circuit 560 in this Application Example will bedescribed in detail.

For each of the channels Ch₁ to Ch_(M), the memory 531 in the signalprocessing circuit 560 stores a digital signal which is output from theA/D converter 587. The memory 531 may be composed of a generic storagemedium such as a semiconductor memory or a hard disk and/or an opticaldisk.

The reception intensity calculation section 532 applies Fouriertransform to the respective beat signals for the channels Ch₁ to Ch_(M)(shown in the lower graph of FIG. 43) that are stored in the memory 531.In the present specification, the amplitude of a piece of complex numberdata after the Fourier transform is referred to as “signal intensity”.The reception intensity calculation section 532 converts the complexnumber data of a reception signal from one of the plurality of antennaelements, or a sum of the complex number data of all reception signalsfrom the plurality of antenna elements, into a frequency spectrum. Inthe resultant spectrum, beat frequencies corresponding to respectivepeak values, which are indicative of presence and distance of targets(preceding vehicles), can be detected. Taking a sum of the complexnumber data of the reception signals from all antenna elements willallow the noise components to average out, whereby the S/N ratio isimproved.

In the case where there is one target, i.e., one preceding vehicle, asshown in FIG. 44, the Fourier transform will produce a spectrum havingone peak value in a period of increasing frequency (the “ascent” period)and one peak value in a period of decreasing frequency (“the descent”period). The beat frequency of the peak value in the “ascent” period isdenoted by “fu”, whereas the beat frequency of the peak value in the“descent” period is denoted by “fd”.

From the signal intensities of beat frequencies, the reception intensitycalculation section 532 detects any signal intensity that exceeds apredefined value (threshold value), thus determining the presence of atarget. Upon detecting a signal intensity peak, the reception intensitycalculation section 532 outputs the beat frequencies (fu, fd) of thepeak values to the distance detection section 533 and the velocitydetection section 534 as the frequencies of the object of interest. Thereception intensity calculation section 532 outputs informationindicating the frequency modulation width Δf to the distance detectionsection 533, and outputs information indicating the center frequency f0to the velocity detection section 534.

In the case where signal intensity peaks corresponding to plural targetsare detected, the reception intensity calculation section 532 findassociations between the ascents peak values and the descent peak valuesbased on predefined conditions. Peaks which are determined as belongingto signals from the same target are given the same number, and thus arefed to the distance detection section 533 and the velocity detectionsection 534.

When there are plural targets, after the Fourier transform, as manypeaks as there are targets will appear in the ascent portions and thedescent portions of the beat signal. In proportion to the distancebetween the radar and a target, the reception signal will become moredelayed and the reception signal in FIG. 43 will shift more toward theright. Therefore, a beat signal will have a greater frequency as thedistant between the target and the radar increases.

Based on the beat frequencies fu and fd which are input from thereception intensity calculation section 532, the distance detectionsection 533 calculates a distance R through the equation below, andsupplies it to the target link processing section 537.

R={c·T/(2·Δf)}·{(fu+fd)/2}

Moreover, based on the beat frequencies fu and fd being input from thereception intensity calculation section 532, the velocity detectionsection 534 calculates a relative velocity V through the equation below,and supplies it to the target link processing section 537.

V={c/(2·f0)}·{(fu−fd)/2}

In the equation which calculates the distance R and the relativevelocity V, c is velocity of light, and T is the modulation period.

Note that the lower limit resolution of distance R is expressed asc/(2Δf). Therefore, as Δf increases, the resolution of distance Rincreases. In the case where the frequency f0 is in the 76 GHz band,when Δf is set on the order of 660 megahertz (MHz), the resolution ofdistance R will be on the order of 0.23 meters (m), for example.Therefore, if two preceding vehicles are traveling abreast of eachother, it may be difficult with the FMCW method to identify whetherthere is one vehicle or two vehicles. In such a case, it might bepossible to run an algorithm for direction-of-arrival estimation thathas an extremely high angular resolution to separate between theazimuths of the two preceding vehicles and enable detection.

By utilizing phase differences between signals from the antenna elements11 ₁, 11 ₂, . . . , 11 _(M), the DBF processing section 535 allows theincoming complex data corresponding to the respective antenna elements,which has been Fourier transformed with respect to the time axis, to beFourier transformed with respect to the direction in which the antennaelements are arrayed. Then, the DBF processing section 535 calculatesspatial complex number data indicating the spectrum intensity for eachangular channel as determined by the angular resolution, and outputs itto the azimuth detection section 536 for the respective beatfrequencies.

The azimuth detection section 536 is provided for the purpose ofestimating the azimuth of a preceding vehicle. Among the values ofspatial complex number data that has been calculated for the respectivebeat frequencies, the azimuth detection section 536 chooses an angle θthat takes the largest value, and outputs it to the target linkprocessing section 537 as the azimuth at which an object of interestexists.

Note that the method of estimating the angle θ indicating the directionof arrival of an arriving wave is not limited to this example. Variousalgorithms for direction-of-arrival estimation that have been mentionedearlier can be employed.

The target link processing section 537 calculates absolute values of thedifferences between the respective values of distance, relativevelocity, and azimuth of the object of interest as calculated in thecurrent cycle and the respective values of distance, relative velocity,and azimuth of the object of interest as calculated 1 cycle before,which are read from the memory 531. Then, if the absolute value of eachdifference is smaller than a value which is defined for the respectivevalue, the target link processing section 537 determines that the targetthat was detected 1 cycle before and the target detected in the currentcycle are an identical target. In that case, the target link processingsection 537 increments the count of target link processes, which is readfrom the memory 531, by one.

If the absolute value of a difference is greater than predetermined, thetarget link processing section 537 determines that a new object ofinterest has been detected. The target link processing section 537stores the respective values of distance, relative velocity, and azimuthof the object of interest as calculated in the current cycle and alsothe count of target link processes for that object of interest to thememory 531.

In the signal processing circuit 560, the distance to the object ofinterest and its relative velocity can be detected by using a spectrumwhich is obtained through a frequency analysis of beat signals, whichare signals generated based on received reflected waves.

The matrix generation section 538 generates a spatial covariance matrixby using the respective beat signals for the channels Ch₁ to Ch_(M)(lower graph in FIG. 43) stored in the memory 531. In the spatialcovariance matrix of Math. 4, each component is the value of a beatsignal which is expressed in terms of real and imaginary parts. Thematrix generation section 538 further determines eigenvalues of thespatial covariance matrix Rxx, and inputs the resultant eigenvalueinformation to the arriving wave estimation unit AU.

When a plurality of signal intensity peaks corresponding to pluralobjects of interest have been detected, the reception intensitycalculation section 532 numbers the peak values respectively in theascent portion and in the descent portion, beginning from those withsmaller frequencies first, and output them to the target outputprocessing section 539. In the ascent and descent portions, peaks of anyidentical number correspond to the same object of interest. Theidentification numbers are to be regarded as the numbers assigned to theobjects of interest. For simplicity of illustration, a leader line fromthe reception intensity calculation section 532 to the target outputprocessing section 539 is conveniently omitted from FIG. 42.

When the object of interest is a structure ahead, the target outputprocessing section 539 outputs the identification number of that objectof interest as indicating a target. When receiving results ofdetermination concerning plural objects of interest, such that all ofthem are structures ahead, the target output processing section 539outputs the identification number of an object of interest that is inthe lane of the driver's vehicle as the object position informationindicating where a target is. Moreover, When receiving results ofdetermination concerning plural objects of interest, such that all ofthem are structures ahead and that two or more objects of interest arein the lane of the driver's vehicle, the target output processingsection 539 outputs the identification number of an object of interestthat is associated with the largest count of target being read from thelink processes memory 531 as the object position information indicatingwhere a target is.

Referring back to FIG. 41, an example where the onboard radar system 510is incorporated in the exemplary construction shown in FIG. 41 will bedescribed. The image processing circuit 720 acquires information of anobject from the video, and detects target position information from theobject information. For example, the image processing circuit 720 isconfigured to estimate distance information of an object by detectingthe depth value of an object within an acquired video, or detect sizeinformation and the like of an object from characteristic amounts in thevideo, thus detecting position information of the object.

The selection circuit 596 selectively feeds position information whichis received from the signal processing circuit 560 or the imageprocessing circuit 720 to the travel assistance electronic controlapparatus 520. For example, the selection circuit 596 compares a firstdistance, i.e., the distance from the driver's vehicle to a detectedobject as contained in the object position information from the signalprocessing circuit 560, against a second distance, i.e., the distancefrom the driver's vehicle to the detected object as contained in theobject position information from the image processing circuit 720, anddetermines which is closer to the driver's vehicle. For example, basedon the result of determination, the selection circuit 596 may select theobject position information which indicates a closer distance to thedriver's vehicle, and output it to the travel assistance electroniccontrol apparatus 520. If the result of determination indicates thefirst distance and the second distance to be of the same value, theselection circuit 596 may output either one, or both of them, to thetravel assistance electronic control apparatus 520.

If information indicating that there is no prospective target is inputfrom the reception intensity calculation section 532, the target outputprocessing section 539 (FIG. 42) outputs zero, indicating that there isno target, as the object position information. Then, on the basis of theobject position information from the target output processing section539, through comparison against a predefined threshold value, theselection circuit 596 chooses either the object position informationfrom the signal processing circuit 560 or the object positioninformation from the image processing circuit 720 to be used.

Based on predefined conditions, the travel assistance electronic controlapparatus 520 having received the position information of a precedingobject from the object detection apparatus 570 performs control to makethe operation safer or easier for the driver who is driving the driver'svehicle, in accordance with the distance and size indicated by theobject position information, the velocity of the driver's vehicle, roadsurface conditions such as rainfall, snowfall or clear weather, or otherconditions. For example, if the object position information indicatesthat no object has been detected, the travel assistance electroniccontrol apparatus 520 may send a control signal to an acceleratorcontrol circuit 526 to increase speed up to a predefined velocity,thereby controlling the accelerator control circuit 526 to make anoperation that is equivalent to stepping on the accelerator pedal.

In the case where the object position information indicates that anobject has been detected, if it is found to be at a predetermineddistance from the driver's vehicle, the travel assistance electroniccontrol apparatus 520 controls the brakes via a brake control circuit524 through a brake-by-wire construction or the like. In other words, itmakes an operation of decreasing the velocity to maintain a constantvehicular gap. Upon receiving the object position information, thetravel assistance electronic control apparatus 520 sends a controlsignal to an alarm control circuit 522 so as to control lampillumination or control audio through a loudspeaker which is providedwithin the vehicle, so that the driver is informed of the nearing of apreceding object. Upon receiving object position information including aspatial distribution of preceding vehicles, the travel assistanceelectronic control apparatus 520 may, if the traveling velocity iswithin a predefined range, automatically make the steering wheel easierto operate to the right or left, or control the hydraulic pressure onthe steering wheel side so as to force a change in the direction of thewheels, thereby providing assistance in collision avoidance with respectto the preceding object.

The object detection apparatus 570 may be arranged so that, if a pieceof object position information which was being continuously detected bythe selection circuit 596 for a while in the previous detection cyclebut which is not detected in the current detection cycle becomesassociated with a piece of object position information from acamera-detected video indicating a preceding object, then continuedtracking is chosen, and object position information from the signalprocessing circuit 560 is output with priority.

An exemplary specific construction and an exemplary operation for theselection circuit 596 to make a selection between the outputs from thesignal processing circuit 560 and the image processing circuit 720 aredisclosed in the specification of U.S. Pat. No. 8,446,312, thespecification of U.S. Pat. No. 8,730,096, and the specification of U.S.Pat. No. 8,730,099. The entire disclosure thereof is incorporated hereinby reference.

[First Variant]

In the radar system for onboard use of the above Application Example,the (sweep) condition for a single instance of FMCW (Frequency ModulatedContinuous Wave) frequency modulation, i.e., a time span required forsuch a modulation (sweep time), is e.g. 1 millisecond, although thesweep time could be shortened to about 100 microseconds.

However, in order to realize such a rapid sweep condition, not only theconstituent elements involved in the radiation of a transmission wave,but also the constituent elements involved in the reception under thatsweep condition must also be able to rapidly operate. For example, anA/D converter 587 (FIG. 42) which rapidly operates under that sweepcondition will be needed. The sampling frequency of the A/D converter587 may be 10 MHz, for example. The sampling frequency may be fasterthan 10 MHz.

In the present variant, a relative velocity with respect to a target iscalculated without utilizing any Doppler shift-based frequencycomponent. In this variant, the sweep time is Tm=100 microseconds, whichis very short. The lowest frequency of a detectable beat signal, whichis 1/Tm, equals 10 kHz in this case. This would correspond to a Dopplershift of a reflected wave from a target which has a relative velocity ofapproximately 20 m/second. In other words, so long as one relies on aDoppler shift, it would be impossible to detect relative velocities thatare equal to or smaller than this. Thus, a method of calculation whichis different from a Doppler shift-based method of calculation ispreferably adopted.

As an example, this variant illustrates a process that utilizes a signal(upbeat signal) representing a difference between a transmission waveand a reception wave which is obtained in an upbeat (ascent) portionwhere the transmission wave increases in frequency. A single sweep timeof FMCW is 100 microseconds, and its waveform is a sawtooth shape whichis composed only of an upbeat portion. In other words, in this variant,the signal wave which is generated by the triangular wave/CW wavegeneration circuit 581 has a sawtooth shape. The sweep width infrequency is 500 MHz. Since no peaks are to be utilized that areassociated with Doppler shifts, the process is not one that generates anupbeat signal and a downbeat signal to utilize the peaks of both, butwill rely on only one of such signals. Although a case of utilizing anupbeat signal will be illustrated herein, a similar process can also beperformed by using a downbeat signal.

The A/D converter 587 (FIG. 42) samples each upbeat signal at a samplingfrequency of 10 MHz, and outputs several hundred pieces of digital data(hereinafter referred to as “sampling data”). The sampling data isgenerated based on upbeat signals after a point in time where areception wave is obtained and until a point in time at which atransmission wave completes transmission, for example. Note that theprocess may be ended as soon as a certain number of pieces of samplingdata are obtained.

In this variant, 128 upbeat signals are transmitted/received in series,for each of which some several hundred pieces of sampling data areobtained. The number of upbeat signals is not limited to 128. It may be256, or 8. An arbitrary number may be selected depending on the purpose.

The resultant sampling data is stored to the memory 531. The receptionintensity calculation section 532 applies a two-dimensional fast Fouriertransform (FFT) to the sampling data. Specifically, first, for each ofthe sampling data pieces that have been obtained through a single sweep,a first FFT process (frequency analysis process) is performed togenerate a power spectrum. Next, the velocity detection section 534performs a second FFT process for the processing results that have beencollected from all sweeps.

When the reflected waves are from the same target, peak components inthe power spectrum to be detected in each sweep period will be of thesame frequency. On the other hand, for different targets, the peakcomponents will differ in frequency. Through the first FFT process,plural targets that are located at different distances can be separated.

In the case where a relative velocity with respect to a target isnon-zero, the phase of the upbeat signal changes slightly from sweep tosweep. In other words, through the second FFT process, a power spectrumwhose elements are the data of frequency components that are associatedwith such phase changes will be obtained for the respective results ofthe first FFT process.

The reception intensity calculation section 532 extracts peak values inthe second power spectrum above, and sends them to the velocitydetection section 534.

The velocity detection section 534 determines a relative velocity fromthe phase changes. For example, suppose that a series of obtained upbeatsignals undergo phase changes by every phase θ [RXd]. Assuming that thetransmission wave has an average wavelength λ, this means there is aλ/(4π/θ) change in distance every time an upbeat signal is obtained.Since this change has occurred over an interval of upbeat signaltransmission Tm (=100 microseconds), the relative velocity is determinedto be {λ/(4π/θ)}/Tm.

Through the above processes, a relative velocity with respect to atarget as well as a distance from the target can be obtained.

[Second Variant]

The radar system 510 is able to detect a target by using a continuouswave(s) CW of one or plural frequencies. This method is especiallyuseful in an environment where a multitude of reflected waves impinge onthe radar system 510 from still objects in the surroundings, e.g., whenthe vehicle is in a tunnel.

The radar system 510 has an antenna array for reception purposes,including five channels of independent reception elements. In such aradar system, the azimuth-of-arrival estimation for incident reflectedwaves is only possible if there are four or fewer reflected waves thatare simultaneously incident. In an FMCW-type radar, the number ofreflected waves to be simultaneously subjected to an azimuth-of-arrivalestimation can be reduced by exclusively selecting reflected waves froma specific distance. However, in an environment where a large number ofstill objects exist in the surroundings, e.g., in a tunnel, it is as ifthere were a continuum of objects to reflect radio waves; therefore,even if one narrows down on the reflected waves based on distance, thenumber of reflected waves may still not be equal to or smaller thanfour. However, any such still object in the surroundings will have anidentical relative velocity with respect to the driver's vehicle, andthe relative velocity will be greater than that associated with anyother vehicle that is traveling ahead. On this basis, such still objectscan be distinguished from any other vehicle based on the magnitudes ofDoppler shifts.

Therefore, the radar system 510 performs a process of: radiatingcontinuous waves CW of plural frequencies; and, while ignoring Dopplershift peaks that correspond to still objects in the reception signals,detecting a distance by using a Doppler shift peak(s) of any smallershift amount(s). Unlike in the FMCW method, in the CW method, afrequency difference between a transmission wave and a reception wave isascribable only to a Doppler shift. In other words, any peak frequencythat appears in a beat signal is ascribable only to a Doppler shift.

In the description of this variant, too, a continuous wave to be used inthe CW method will be referred to as a “continuous wave CW”. Asdescribed above, a continuous wave CW has a constant frequency; that is,it is unmodulated.

Suppose that the radar system 510 has radiated a continuous wave CW of afrequency fp, and detected a reflected wave of a frequency fq that hasbeen reflected off a target. The difference between the transmissionfrequency fp and the reception frequency fq is called a Dopplerfrequency, which approximates to fp−fq=2·Vr·fp/c. Herein, Vr is arelative velocity between the radar system and the target, and c is thevelocity of light. The transmission frequency fp, the Doppler frequency(fp−fq), and the velocity of light c are known. Therefore, from thisequation, the relative velocity Vr=(fp−fq)·c/2fp can be determined. Thedistance to the target is calculated by utilizing phase information aswill be described later.

In order to detect a distance to a target by using continuous waves CW,a 2 frequency CW method is adopted. In the 2 frequency CW method,continuous waves CW of two frequencies which are slightly apart areradiated each for a certain period, and their respective reflected wavesare acquired. For example, in the case of using frequencies in the 76GHz band, the difference between the two frequencies would be severalhundred kHz. As will be described later, it is more preferable todetermine the difference between the two frequencies while taking intoaccount the minimum distance at which the radar used is able to detect atarget.

Suppose that the radar system 510 has sequentially radiated continuouswaves CW of frequencies fp1 and fp2 (fp1<fp2), and that the twocontinuous waves CW have been reflected off a single target, resultingin reflected waves of frequencies fq1 and fq2 being received by theradar system 510.

Based on the continuous wave CW of the frequency fp1 and the reflectedwave (frequency fq1) thereof, a first Doppler frequency is obtained.Based on the continuous wave CW of the frequency fp2 and the reflectedwave (frequency fq2) thereof, a second Doppler frequency is obtained.The two Doppler frequencies have substantially the same value. However,due to the difference between the frequencies fp1 and fp2, the complexsignals of the respective reception waves differ in phase. By utilizingthis phase information, a distance (range) to the target can becalculated.

Specifically, the radar system 510 is able to determine the distance Ras R=c·Δφ/4π(fp2−fp1). Herein, Δφ denotes the phase difference betweentwo beat signals, i.e., beat signal 1 which is obtained as a differencebetween the continuous wave CW of the frequency fp1 and the reflectedwave (frequency fq1) thereof and beat signal 2 which is obtained as adifference between the continuous wave CW of the frequency fp2 and thereflected wave (frequency fq2) thereof. The method of identifying thefrequency fb1 of beat signal 1 and the frequency fb2 of beat signal 2 isidentical to that in the aforementioned instance of a beat signal from acontinuous wave CW of a single frequency.

Note that a relative velocity Vr under the 2 frequency CW method isdetermined as follows.

Vr=fb1·c/2·fp1 or Vr=fb2·c/2·fp2

Moreover, the range in which a distance to a target can be uniquelyidentified is limited to the range defined by Rmax<c/2(fp2−fp1). Thereason is that beat signals resulting from a reflected wave from anyfarther target would produce a Δφ which is greater than 2n, such thatthey are indistinguishable from beat signals associated with targets atcloser positions. Therefore, it is more preferable to adjust thedifference between the frequencies of the two continuous waves CW sothat Rmax becomes greater than the minimum detectable distance of theradar. In the case of a radar whose minimum detectable distance is 100m, fp2−fp1 may be made e.g. 1.0 MHz. In this case, Rmax=150 m, so that asignal from any target from a position beyond Rmax is not detected. Inthe case of mounting a radar which is capable of detection up to 250 m,fp2−fp1 may be made e.g. 500 kHz. In this case, Rmax=300 m, so that asignal from any target from a position beyond Rmax is not detected,either. In the case where the radar has both of an operation mode inwhich the minimum detectable distance is 100 m and the horizontalviewing angle is 120 degrees and an operation mode in which the minimumdetectable distance is 250 m and the horizontal viewing angle is 5degrees, it is preferable to switch the fp2−fp1 value be 1.0 MHz and 500kHz for operation in the respective operation modes.

A detection approach is known which, by transmitting continuous waves CWat N different frequencies (where N is an integer of 3 or more), andutilizing phase information of the respective reflected waves, detects adistance to each target. Under this detection approach, distance can beproperly recognized up to N−1 targets. As the processing to enable this,a fast Fourier transform (FFT) is used, for example. Given N=64 or 128,an FFT is performed for sampling data of a beat signal as a differencebetween a transmission signal and a reception signal for each frequency,thus obtaining a frequency spectrum (relative velocity). Thereafter, atthe frequency of the CW wave, a further FFT is performed for peaks ofthe same frequency, thus to derive distance information.

Hereinafter, this will be described more specifically.

For ease of explanation, first, an instance will be described wheresignals of three frequencies f1, f2 and f3 are transmitted while beingswitched over time. It is assumed that f1>f2>f3, and f1−f2=f2−f3=Δf. Atransmission time Δt is assumed for the signal wave for each frequency.FIG. 46 shows a relationship between three frequencies f1, f2 and f3.

Via the transmission antenna Tx, the triangular wave/CW wave generationcircuit 581 (FIG. 42) transmits continuous waves CW of frequencies f1,f2 and f3, each lasting for the time Δt. The reception antennas Rxreceive reflected waves resulting by the respective continuous waves CWbeing reflected off one or plural targets.

Each mixer 584 mixes a transmission wave and a reception wave togenerate a beat signal. The A/D converter 587 converts the beat signal,which is an analog signal, into several hundred pieces of digital data(sampling data), for example.

Using the sampling data, the reception intensity calculation section 532performs FFT computation. Through the FFT computation, frequencyspectrum information of reception signals is obtained for the respectivetransmission frequencies f1, f2 and f3.

Thereafter, the reception intensity calculation section 532 separatespeak values from the frequency spectrum information of the receptionsignals. The frequency of any peak value which is predetermined orgreater is in proportion to a relative velocity with respect to atarget. Separating a peak value(s) from the frequency spectruminformation of reception signals is synonymous with separating one orplural targets with different relative velocities.

Next, with respect to each of the transmission frequencies f1 to f3, thereception intensity calculation section 532 measures spectruminformation of peak values of the same relative velocity or relativevelocities within a predefined range.

Now, consider a scenario where two targets A and B exist which haveabout the same relative velocity but are at respectively differentdistances. A transmission signal of the frequency f1 will be reflectedfrom both of targets A and B to result in reception signals beingobtained. The reflected waves from targets A and B will result insubstantially the same beat signal frequency. Therefore, the powerspectra at the Doppler frequencies of the reception signals,corresponding to their relative velocities, are obtained as a syntheticspectrum F1 into which the power spectra of two targets A and B havebeen merged.

Similarly, for each of the frequencies f2 and f3, the power spectra atthe Doppler frequencies of the reception signals, corresponding to theirrelative velocities, are obtained as a synthetic spectrum F1 into whichthe power spectra of two targets A and B have been merged.

FIG. 47 shows a relationship between synthetic spectra F1 to F3 on acomplex plane. In the directions of the two vectors composing each ofthe synthetic spectra F1 to F3, the right vector corresponds to thepower spectrum of a reflected wave from target A; i.e., vectors f1A, f2Aand f3A, in FIG. 47. On the other hand, in the directions of the twovectors composing each of the synthetic spectra F1 to F3, the leftvector corresponds to the power spectrum of a reflected wave from targetB; i.e., vectors f1B, f2B and f3B in FIG. 47.

Under a constant difference Δf between the transmission frequencies, thephase difference between the reception signals corresponding to therespective transmission signals of the frequencies f1 and f2 is inproportion to the distance to a target. Therefore, the phase differencebetween the vectors f1A and f2A and the phase difference between thevectors f2A and f3A are of the same value θA, this phase difference θAbeing in proportion to the distance to target A. Similarly, the phasedifference between the vectors f1B and f2B and the phase differencebetween the vectors f2B and f3B are of the same value θB, this phasedifference θB being in proportion to the distance to target B.

By using a well-known method, the respective distances to targets A andB can be determined from the synthetic spectra F1 to F3 and thedifference Δf between the transmission frequencies. This technique isdisclosed in U.S. Pat. No. 6,703,967, for example. The entire disclosureof this publication is incorporated herein by reference.

Similar processing is also applicable when the transmitted signals havefour or more frequencies.

Note that, before transmitting continuous waves CW at N differentfrequencies, a process of determining the distance to and relativevelocity of each target may be performed by the 2 frequency CW method.Then, under predetermined conditions, this process may be switched to aprocess of transmitting continuous waves CW at N different frequencies.For example, FFT computation may be performed by using the respectivebeat signals at the two frequencies, and if the power spectrum of eachtransmission frequency undergoes a change over time of 30% or more, theprocess may be switched. The amplitude of a reflected wave from eachtarget undergoes a large change over time due to multipath influencesand the like. When there exists a change of a predetermined magnitude orgreater, it may be considered that plural targets may exist.

Moreover, the CW method is known to be unable to detect a target whenthe relative velocity between the radar system and the target is zero,i.e., when the Doppler frequency is zero. However, when a pseudo Dopplersignal is determined by the following methods, for example, it ispossible to detect a target by using that frequency.

(Method 1) A mixer that causes a certain frequency shift in the outputof a receiving antenna is added. By using a transmission signal and areception signal with a shifted frequency, a pseudo Doppler signal canbe obtained.

(Method 2) A variable phase shifter to introduce phase changescontinuously over time is inserted between the output of a receivingantenna and a mixer, thus adding a pseudo phase difference to thereception signal. By using a transmission signal and a reception signalwith an added phase difference, a pseudo Doppler signal can be obtained.

An example of specific construction and operation of inserting avariable phase shifter to generate a pseudo Doppler signal under Method2 is disclosed in Japanese Laid-Open Patent Publication No. 2004-257848.The entire disclosure of this publication is incorporated herein byreference.

When targets with zero or very little relative velocity need to bedetected, the aforementioned processes of generating a pseudo Dopplersignal may be adopted, or the process may be switched to a targetdetection process under the FMCW method.

Next, with reference to FIG. 48, a procedure of processing to beperformed by the object detection apparatus 570 of the onboard radarsystem 510 will be described.

The example below will illustrate a case where continuous waves CW aretransmitted at two different frequencies fp1 and fp2 (fp1<fp2), and thephase information of each reflected wave is utilized to respectivelydetect a distance with respect to a target.

FIG. 48 is a flowchart showing the procedure of a process of determiningrelative velocity and distance according to this variant.

At step S41, the triangular wave/CW wave generation circuit 581generates two continuous waves CW of frequencies which are slightlyapart, i.e., frequencies fp1 and fp2.

At step S42, the transmission antenna Tx and the reception antennas Rxperform transmission/reception of the generated series of continuouswaves CW. Note that the process of step S41 and the process of step S42are to be performed in parallel fashion respectively by the triangularwave/CW wave generation circuit 581 and the transmission antennaTx/reception antenna Rx, rather than step S42 following only aftercompletion of step S41.

At step S43, each mixer 584 generates a difference signal by utilizingeach transmission wave and each reception wave, whereby two differencesignals are obtained. Each reception wave is inclusive of a receptionwave emanating from a still object and a reception wave emanating from atarget. Therefore, next, a process of identifying frequencies to beutilized as the beat signals is performed. Note that the process of stepS41, the process of step S42, and the process of step S43 are to beperformed in parallel fashion by the triangular wave/CW wave generationcircuit 581, the transmission antenna Tx/reception antenna Rx, and themixers 584, rather than step S42 following only after completion of stepS41, or step S43 following only after completion of step S42.

At step S44, for each of the two difference signals, the objectdetection apparatus 570 identifies certain peak frequencies to befrequencies fb1 and fb2 of beat signals, such that these frequencies areequal to or smaller than a frequency which is predefined as a thresholdvalue and yet they have amplitude values which are equal to or greaterthan a predetermined amplitude value, and that the difference betweenthe two frequencies is equal to or smaller than a predetermined value.

At step S45, based on one of the two beat signal frequencies identified,the reception intensity calculation section 532 detects a relativevelocity. The reception intensity calculation section 532 calculates therelative velocity according to Vr=fb1·c/2·fp1, for example. Note that arelative velocity may be calculated by utilizing each of the two beatsignal frequencies, which will allow the reception intensity calculationsection 532 to verify whether they match or not, thus enhancing theprecision of relative velocity calculation.

At step S46, the reception intensity calculation section 532 determinesa phase difference Δφ between two beat signals 1 and 2, and determines adistance R=c·Δφ/4π(fp2−fp1) to the target.

Through the above processes, the relative velocity and distance to atarget can be detected.

Note that continuous waves CW may be transmitted at N differentfrequencies (where N is 3 or more), and by utilizing phase informationof the respective reflected wave, distances to plural targets which areof the same relative velocity but at different positions may bedetected.

In addition to the radar system 510, the vehicle 500 described above mayfurther include another radar system. For example, the vehicle 500 mayfurther include a radar system having a detection range toward the rearor the sides of the vehicle body. In the case of incorporating a radarsystem having a detection range toward the rear of the vehicle body, theradar system may monitor the rear, and if there is any danger of havinganother vehicle bump into the rear, make a response by issuing an alarm,for example. In the case of incorporating a radar system having adetection range toward the sides of the vehicle body, the radar systemmay monitor an adjacent lane when the driver's vehicle changes its lane,etc., and make a response by issuing an alarm or the like as necessary.

The applications of the above-described radar system 510 are not limitedto onboard use only. Rather, the radar system 510 may be used as sensorsfor various purposes. For example, it may be used as a radar formonitoring the surroundings of a house or any other building.Alternatively, it may be used as a sensor for detecting the presence orabsence of a person at a specific indoor place, or whether or not such aperson is undergoing any motion, etc., without utilizing any opticalimages.

[Supplementary Details of Processing]

Other example embodiments will be described in connection with the 2frequency CW or FMCW techniques for array antennas as described above.As described earlier, in the example of FIG. 42, the reception intensitycalculation section 532 applies a Fourier transform to the respectivebeat signals for the channels Ch₁ to Ch_(M) (lower graph in FIG. 43)stored in the memory 531. These beat signals are complex signals, inorder that the phase of the signal of computational interest beidentified. This allows the direction of an arriving wave to beaccurately identified. In this case, however, the computational load forFourier transform increases, thus calling for a larger-scaled circuit.

In order to solve this problem, a scalar signal may be generated as abeat signal. For each of a plurality of beat signals that have beengenerated, two complex Fourier transforms may be performed with respectto the spatial axis direction, which conforms to the antenna array, andto the time axis direction, which conforms to the lapse of time, thus toobtain results of frequency analysis. As a result, with only a smallamount of computation, beam formation can eventually be achieved so thatdirections of arrival of reflected waves can be identified, wherebyresults of frequency analysis can be obtained for the respective beams.As a patent document related to the present disclosure, the entiredisclosure of the specification of U.S. Pat. No. 6,339,395 isincorporated herein by reference.

[Optical Sensor, e.g., Camera, and Millimeter Wave Radar]

Next, a comparison between the above-described array antenna andconventional antennas, as well as an exemplary application in which bothof the present array antenna and an optical sensor (e.g., a camera) areutilized, will be described. Note that LIDAR or the like may be employedas the optical sensor.

A millimeter wave radar is able to directly detect a distance (range) toa target and a relative velocity thereof. Another characteristic is thatits detection performance is not much deteriorated in the nighttime(including dusk), or in bad weather, e.g., rainfall, fog, or snowfall.On the other hand, it is believed that it is not just as easy for amillimeter wave radar to take a two-dimensional grasp of a target as itis for a camera. On the other hand, it is relatively easy for a camerato take a two-dimensional grasp of a target and recognize its shape.However, a camera may not be able to image a target in nighttime or badweather, which presents a considerable problem. This problem isparticularly outstanding when droplets of water have adhered to theportion through which to ensure lighting, or the eyesight is narrowed bya fog. This problem similarly exists for LIDAR or the like, which alsopertains to the realm of optical sensors.

In these years, in answer to increasing demand for safer vehicleoperation, driver assist systems for preventing collisions or the likeare being developed. A driver assist system acquires an image in thedirection of vehicle travel with a sensor such as a camera or amillimeter wave radar, and when any obstacle is recognized that ispredicted to hinder vehicle travel, brakes or the like are automaticallyapplied to prevent collisions or the like. Such a function of collisionavoidance is expected to operate normally, even in nighttime or badweather.

Hence, driver assist systems of a so-called fusion construction aregaining prevalence, where, in addition to a conventional optical sensorsuch as a camera, a millimeter wave radar is mounted as a sensor, thusrealizing a recognition process that takes advantage of both. Such adriver assist system will be discussed later.

On the other hand, higher and higher functions are being required of themillimeter wave radar itself. A millimeter wave radar for onboard usemainly uses electromagnetic waves of the 76 GHz band. The antenna powerof its antenna is restricted to below a certain level under eachcountry's law or the like. For example, it is restricted to 0.01 W orbelow in Japan. Under such restrictions, a millimeter wave radar foronboard use is expected to satisfy the required performance that, forexample, its detection range is 200 m or more; the antenna size is 60mm×60 mm or less; its horizontal detection angle is 90 degrees or more;its range resolution is 20 cm or less; it is capable of short-rangedetection within 10 m; and so on. Conventional millimeter wave radarshave used microstrip lines as waveguides, and patch antennas as antennas(hereinafter, these will both be referred to as “patch antennas”).However, with a patch antenna, it has been difficult to attain theaforementioned performance.

By using a slot array antenna to which the technique of the presentdisclosure is applied, the inventors have successfully achieved theaforementioned performance. As a result, a millimeter wave radar hasbeen realized which is smaller in size, more efficient, andhigher-performance than are conventional patch antennas and the like. Inaddition, by combining this millimeter wave radar and an optical sensorsuch as a camera, a small-sized, highly efficient, and high-performancefusion apparatus has been realized which has existed never before. Thiswill be described in detail below.

FIG. 49 is a diagram concerning a fusion apparatus in a vehicle 500, thefusion apparatus including an onboard camera system 700 and a radarsystem 510 (hereinafter referred to also as the millimeter wave radar510) having a slot array antenna to which the technique of the presentdisclosure is applied. With reference to this figure, various exampleembodiments will be described below.

[Installment of Millimeter Wave Radar within Vehicle Room]

A conventional patch antenna-based millimeter wave radar 510′ is placedbehind and inward of a grill 512 which is at the front nose of avehicle. An electromagnetic wave that is radiated from an antenna goesthrough the apertures in the grill 512, and is radiated ahead of thevehicle 500. In this case, no dielectric layer, e.g., glass, exists thatdecays or reflects electromagnetic wave energy, in the region throughwhich the electromagnetic wave passes. As a result, an electromagneticwave that is radiated from the patch antenna-based millimeter wave radar510′ reaches over a long range, e.g., to a target which is 150 m orfarther away. By receiving with the antenna the electromagnetic wavereflected therefrom, the millimeter wave radar 510′ is able to detect atarget. In this case, however, since the antenna is placed behind andinward of the grill 512 of the vehicle, the radar may be broken when thevehicle collides into an obstacle. Moreover, it may be soiled with mudor the like in rain, etc., and the soil that has adhered to the antennamay hinder radiation and reception of electromagnetic waves.

Similarly to the conventional manner, the millimeter wave radar 510incorporating a slot array antenna according to an example embodiment ofthe present disclosure may be placed behind the grill 512, which islocated at the front nose of the vehicle (not shown). This allows theenergy of the electromagnetic wave to be radiated from the antenna to beutilized by 100%, thus enabling long-range detection beyond theconventional level, e.g., detection of a target which is at a distanceof 250 m or more.

Furthermore, the millimeter wave radar 510 according to an exampleembodiment of the present disclosure can also be placed within thevehicle room, i.e., inside the vehicle. In that case, the millimeterwave radar 510 is placed inward of the windshield 511 of the vehicle, tofit in a space between the windshield 511 and a face of the rearviewmirror (not shown) that is opposite to its specular surface. On theother hand, the conventional patch antenna-based millimeter wave radar510′ cannot be placed inside the vehicle room mainly for the twofollowing reasons. A first reason is its large size, which preventsitself from being accommodated within the space between the windshield511 and the rearview mirror. A second reason is that an electromagneticwave that is radiated ahead reflects off the windshield 511 and decaysdue to dielectric loss, thus becoming unable to travel the desireddistance. As a result, if a conventional patch antenna-based millimeterwave radar is placed within the vehicle room, only targets which are 100m ahead or less can be detected, for example. On the other hand, amillimeter wave radar according to an example embodiment of the presentdisclosure is able to detect a target which is at a distance of 200 m ormore, despite reflection or decay at the windshield 511. Thisperformance is equivalent to, or even greater than, the case where aconventional patch antenna-based millimeter wave radar is placed outsidethe vehicle room.

[Fusion Construction Based on Millimeter Wave Radar and Camera, Etc.,being Placed within Vehicle Room]

Currently, an optical imaging device such as a CCD camera is used as themain sensor in many a driver assist system (Driver Assist System).Usually, a camera or the like is placed within the vehicle room, inwardof the windshield 511, in order to account for unfavorable influences ofthe external environment, etc. In this context, in order to minimize theoptical effect of raindrops and the like, the camera or the like isplaced in a region which is swept by the wipers (not shown) but isinward of the windshield 511.

In recent years, due to needs for improved performance of a vehicle interms of e.g. automatic braking, there has been a desire for automaticbraking or the like that is guaranteed to work regardless of whateverexternal environment may exist. In this case, if the only sensor in thedriver assist system is an optical device such as a camera, a problemexists in that reliable operation is not guaranteed in nighttime or badweather. This has led to the need for a driver assist system thatincorporates not only an optical sensor (such as a camera) but also amillimeter wave radar, these being used for cooperative processing, sothat reliable operation is achieved even in nighttime or bad weather.

As described earlier, a millimeter wave radar incorporating the presentslot array antenna permits itself to be placed within the vehicle room,due to downsizing and remarkable enhancement in the efficiency of theradiated electromagnetic wave over that of a conventional patch antenna.By taking advantage of these properties, as shown in FIG. 49, themillimeter wave radar 510, which incorporates not only an optical sensor(onboard camera system) 700 such as a camera but also a slot arrayantenna according to the present disclosure, allows both to be placedinward of the windshield 511 of the vehicle 500. This has created thefollowing novel effects.

(1) It is easier to install the driver assist system on the vehicle 500.The conventional patch antenna-based millimeter wave radar 510′ hasrequired a space behind the grill 512, which is at the front nose, inorder to accommodate the radar. Since this space may include some sitesthat affect the structural design of the vehicle, if the size of theradar device is changed, it may have been necessary to reconsider thestructural design. This inconvenience is avoided by placing themillimeter wave radar within the vehicle room.

(2) Free from the influences of rain, nighttime, or other externalenvironment factors to the vehicle, more reliable operation can beachieved. Especially, as shown in FIG. 50, by placing the millimeterwave radar (onboard camera system) 510 and the onboard camera system 700at substantially the same position within the vehicle room, they canattain an identical field of view and line of sight, thus facilitatingthe “matching process” which will be described later, i.e., a processthrough which to establish that respective pieces of target informationcaptured by them actually come from an identical object. On the otherhand, if the millimeter wave radar 510′ were placed behind the grill512, which is at the front nose outside the vehicle room, its radar lineof sight L would differ from a radar line of sight M of the case whereit was placed within the vehicle room, thus resulting in a large offsetwith the image to be acquired by the onboard camera system 700.

(3) Reliability of the millimeter wave radar device is improved. Asdescribed above, since the conventional patch antenna-based millimeterwave radar 510′ is placed behind the grill 512, which is at the frontnose, it is likely to gather soil, and may be broken even in a minorcollision accident or the like. For these reasons, cleaning andfunctionality checks are always needed. Moreover, as will be describedbelow, if the position or direction of attachment of the millimeter waveradar becomes shifted due to an accident or the like, it is necessary toreestablish alignment with respect to the camera. The chances of suchoccurrences are reduced by placing the millimeter wave radar within thevehicle room, whereby the aforementioned inconveniences are avoided.

In a driver assist system of such fusion construction, the opticalsensor, e.g., a camera, and the millimeter wave radar 510 incorporatingthe present slot array antenna may have an integrated construction,i.e., being in fixed position with respect to each other. In that case,certain relative positioning should be kept between the optical axis ofthe optical sensor such as a camera and the directivity of the antennaof the millimeter wave radar, as will be described later. When thisdriver assist system having an integrated construction is fixed withinthe vehicle room of the vehicle 500, the optical axis of the camera,etc., should be adjusted so as to be oriented in a certain directionahead of the vehicle. For these matters, see US Patent ApplicationPublication No. 2015/0264230, US Patent Application Publication No.2016/0264065, U.S. patent application Ser. No. 15/248,141, U.S. patentapplication Ser. No. 15/248,149, and U.S. patent application Ser. No.15/248,156, which are incorporated herein by reference. Relatedtechniques concerning the camera are described in the specification ofU.S. Pat. No. 7,355,524, and the specification of U.S. Pat. No.7,420,159, the entire disclosure of each which is incorporated herein byreference.

Regarding placement of an optical sensor such as a camera and amillimeter wave radar within the vehicle room, see, for example, thespecification of U.S. Pat. No. 8,604,968, the specification of U.S. Pat.No. 8,614,640, and the specification of U.S. Pat. No. 7,978,122, theentire disclosure of each which is incorporated herein by reference.However, at the time when these patents were filed for, onlyconventional antennas with patch antennas were the known millimeter waveradars, and thus observation was not possible over sufficient distances.For example, the distance that is observable with a conventionalmillimeter wave radar is considered to be at most 100 m to 150 m.Moreover, when a millimeter wave radar is placed inward of thewindshield, the large radar size inconveniently blocks the driver'sfield of view, thus hindering safe driving. On the other hand, amillimeter wave radar incorporating a slot array antenna according to anexample embodiment of the present disclosure is capable of being placedwithin the vehicle room because of its small size and remarkableenhancement in the efficiency of the radiated electromagnetic wave overthat of a conventional patch antenna. This enables a long-rangeobservation over 200 m, while not blocking the driver's field of view.

[Adjustment of Position of Attachment Between Millimeter Wave Radar andCamera, Etc.,]

In the processing under fusion construction (which hereinafter may bereferred to as a “fusion process”), it is desired that an image which isobtained with a camera or the like and the radar information which isobtained with the millimeter wave radar map onto the same coordinatesystem because, if they differ as to position and target size,cooperative processing between both will be hindered.

This involves adjustment from the following three standpoints.

(1) The optical axis of the camera or the like and the antennadirectivity of the millimeter wave radar must have a certain fixedrelationship.

It is required that the optical axis of the camera or the like and theantenna directivity of the millimeter wave radar are matched.Alternatively, a millimeter wave radar may include two or moretransmission antennas and two or more reception antennas, thedirectivities of these antennas being intentionally made different.Therefore, it is necessary to guarantee that at least a certain knownrelationship exists between the optical axis of the camera or the likeand the directivities of these antennas.

In the case where the camera or the like and the millimeter wave radarhave the aforementioned integrated construction, i.e., being in fixedposition to each other, the relative positioning between the camera orthe like and the millimeter wave radar stays fixed. Therefore, theaforementioned requirements are satisfied with respect to such anintegrated construction. On the other hand, in a conventional patchantenna or the like, where the millimeter wave radar is placed behindthe grill 512 of the vehicle 500, the relative positioning between themis usually to be adjusted according to (2) below.

(2) A certain fixed relationship exists between an image acquired withthe camera or the like and radar information of the millimeter waveradar in an initial state (e.g., upon shipment) of having been attachedto the vehicle.

The positions of attachment of the optical sensor such as a camera andthe millimeter wave radar 510 or 510′ on the vehicle 500 will finally bedetermined in the following manner. At a predetermined position 800ahead of the vehicle 500, a chart to serve as a reference or a targetwhich is subject to observation by the radar (which will hereinafter bereferred to as, respectively, a “reference chart” and a “referencetarget”, and collectively as the “benchmark”) is accurately positioned.This is observed with an optical sensor such as a camera or with themillimeter wave radar 510. The observation information regarding theobserved benchmark is compared against previously-stored shapeinformation or the like of the benchmark, and the current offsetinformation is quantitated. Based on this offset information, by atleast one of the following means, the positions of attachment of anoptical sensor such as a camera and the millimeter wave radar 510 or510′ are adjusted or corrected. Any other means may also be employedthat can provide similar results.

(i) Adjust the positions of attachment of the camera and the millimeterwave radar so that the benchmark will come at a midpoint between thecamera and the millimeter wave radar. This adjustment may be done byusing a jig or tool, etc., which is separately provided.

(ii) Determine an offset amounts of the camera and the axis/directivityof the millimeter wave radar relative to the benchmark, and throughimage processing of the camera image and radar processing, correct forthese offset amounts in the axis/directivity.

What is to be noted is that, in the case where the optical sensor suchas a camera and the millimeter wave radar 510 incorporating a slot arrayantenna according to an example embodiment of the present disclosurehave an integrated construction, i.e., being in fixed position to eachother, adjusting an offset of either the camera or the radar withrespect to the benchmark will make the offset amount known for the otheras well, thus making it unnecessary to check for the other's offset withrespect to the benchmark.

Specifically, with respect to the onboard camera system 700, a referencechart may be placed at a predetermined position 750, and an image takenby the camera is compared against advance information indicating wherein the field of view of the camera the reference chart image is supposedto be located, thereby detecting an offset amount. Based on this, thecamera is adjusted by at least one of the above means (i) and (ii).Next, the offset amount which has been ascertained for the camera istranslated into an offset amount of the millimeter wave radar.Thereafter, an offset amount adjustment is made with respect to theradar information, by at least one of the above means (i) and (ii).

Alternatively, this may be performed on the basis of the millimeter waveradar 510. In other words, with respect to the millimeter wave radar510, a reference target may be placed at a predetermined position 800,and the radar information thereof is compared against advanceinformation indicating where in the field of view of the millimeter waveradar 510 the reference target is supposed to be located, therebydetecting an offset amount. Based on this, the millimeter wave radar 510is adjusted by at least one of the above means (i) and (ii). Next, theoffset amount which has been ascertained for the millimeter wave radaris translated into an offset amount of the camera. Thereafter, an offsetamount adjustment is made with respect to the image information obtainedby the camera, by at least one of the above means (i) and (ii).

(3) Even after an initial state of the vehicle, a certain relationshipis maintained between an image acquired with the camera or the like andradar information of the millimeter wave radar.

Usually, an image acquired with the camera or the like and radarinformation of the millimeter wave radar are supposed to be fixed in theinitial state, and hardly vary unless in an accident of the vehicle orthe like. However, if an offset in fact occurs between these, anadjustment is possible by the following means.

The camera is attached in such a manner that portions 513 and 514(characteristic points) that are characteristic of the driver's vehiclefit within its field of view, for example. The positions at which thesecharacteristic points are actually imaged by the camera are comparedagainst the information of the positions to be assumed by thesecharacteristic points when the camera is attached accurately in place,and an offset amount(s) is detected therebetween. Based on this detectedoffset amount(s), the position of any image that is taken thereafter maybe corrected, whereby an offset of the physical position of attachmentof the camera can be corrected for. If this correction sufficientlyembodies the performance that is required of the vehicle, then theadjustment per the above (2) may not be needed. By regularly performingthis adjustment during startup or operation of the vehicle 500, even ifan offset of the camera or the like occurs anew, it is possible tocorrect for the offset amount, thus helping safe travel.

However, this means is generally considered to result in poorer accuracyof adjustment than with the above means (2). When making an adjustmentbased on an image which is obtained by imaging a benchmark with thecamera, the azimuth of the benchmark can be determined with a highprecision, whereby a high accuracy of adjustment can be easily achieved.However, since this means utilizes a part of the vehicle body for theadjustment instead of a benchmark, it is rather difficult to enhance theaccuracy of azimuth determination. Thus, the resultant accuracy ofadjustment will be somewhat inferior. However, it may still be effectiveas a means of correction when the position of attachment of the cameraor the like is considerably altered for reasons such as an accident or alarge external force being applied to the camera or the like within thevehicle room, etc.

[Mapping of Target as Detected by Millimeter Wave Radar and Camera orthe Like: Matching Process]

In a fusion process, for a given target, it needs to be established thatan image thereof which is acquired with a camera or the like and radarinformation which is acquired with the millimeter wave radar pertain to“the same target”. For example, suppose that two obstacles (first andsecond obstacles), e.g., two bicycles, have appeared ahead of thevehicle 500. These two obstacles will be captured as camera images, anddetected as radar information of the millimeter wave radar. At thistime, the camera image and the radar information with respect to thefirst obstacle need to be mapped to each other so that they are bothdirected to the same target. Similarly, the camera image and the radarinformation with respect to the second obstacle need to be mapped toeach other so that they are both directed to the same target. If thecamera image of the first obstacle and the radar information of thesecond obstacle are mistakenly recognized to pertain to an identicalobject, a considerable accident may occur. Hereinafter, in the presentspecification, such a process of determining whether a target in thecamera image and a target in the radar image pertain to the same targetmay be referred to as a “matching process”.

This matching process may be implemented by various detection devices(or methods) described below. Hereinafter, these will be specificallydescribed. Note that the each of the following detection devices is tobe installed in the vehicle, and at least includes a millimeter waveradar detection section, an image detection section (e.g., a camera)which is oriented in a direction overlapping the direction of detectionby the millimeter wave radar detection section, and a matching section.Herein, the millimeter wave radar detection section includes a slotarray antenna according to any of the example embodiments of the presentdisclosure, and at least acquires radar information in its own field ofview. The image acquisition section at least acquires image informationin its own field of view. The matching section includes a processingcircuit which matches a result of detection by the millimeter wave radardetection section against a result of detection by the image detectionsection to determine whether or not the same target is being detected bythe two detection sections. Herein, the image detection section may becomposed of a selected one of, or selected two or more of, an opticalcamera, LIDAR, an infrared radar, and an ultrasonic radar. The followingdetection devices differ from one another in terms of the detectionprocess at their respective matching section.

In a first detection device, the matching section performs two matchesas follows. A first match involves, for a target of interest that hasbeen detected by the millimeter wave radar detection section, obtainingdistance information and lateral position information thereof, and alsofinding a target that is the closest to the target of interest among atarget or two or more targets detected by the image detection section,and detecting a combination(s) thereof. A second match involves, for atarget of interest that has been detected by the image detectionsection, obtaining distance information and lateral position informationthereof, and also finding a target that is the closest to the target ofinterest among a target or two or more targets detected by themillimeter wave radar detection section, and detecting a combination(s)thereof. Furthermore, this matching section determines whether there isany matching combination between the combination(s) of such targets asdetected by the millimeter wave radar detection section and thecombination(s) of such targets as detected by the image detectionsection. Then, if there is any matching combination, it is determinedthat the same object is being detected by the two detection sections. Inthis manner, a match is attained between the respective targets thathave been detected by the millimeter wave radar detection section andthe image detection section.

A related technique is described in the specification of U.S. Pat. No.7,358,889, the entire disclosure of which is incorporated herein byreference. In this publication, the image detection section isillustrated by way of a so-called stereo camera that includes twocameras. However, this technique is not limited thereto. In the casewhere the image detection section includes a single camera, detectedtargets may be subjected to an image recognition process or the like asappropriate, in order to obtain distance information and lateralposition information of the targets. Similarly, a laser sensor such as alaser scanner may be used as the image detection section.

In a second detection device, the matching section matches a result ofdetection by the millimeter wave radar detection section and a result ofdetection by the image detection section every predetermined period oftime. If the matching section determines that the same target was beingdetected by the two detection sections in the previous result ofmatching, it performs a match by using this previous result of matching.Specifically, the matching section matches a target which is currentlydetected by the millimeter wave radar detection section and a targetwhich is currently detected by the image detection section, against thetarget which was determined in the previous result of matching to bebeing detected by the two detection sections. Then, based on the resultof matching for the target which is currently detected by the millimeterwave radar detection section and the result of matching for the targetwhich is currently detected by the image detection section, the matchingsection determines whether or not the same target is being detected bythe two detection sections. Thus, rather than directly matching theresults of detection by the two detection sections, this detectiondevice performs a chronological match between the two results ofdetection and a previous result of matching. Therefore, the accuracy ofdetection is improved over the case of only performing a momentarymatch, whereby stable matching is realized. In particular, even if theaccuracy of the detection section drops momentarily, matching is stillpossible because of utilizing past results of matching. Moreover, byutilizing the previous result of matching, this detection device is ableto easily perform a match between the two detection sections.

In the current match which utilizes the previous result of matching, ifthe matching section of this detection device determines that the sameobject is being detected by the two detection sections, then thematching section of this detection device excludes this determinedobject in performing matching between objects which are currentlydetected by the millimeter wave radar detection section and objectswhich are currently detected by the image detection section. Then, thismatching section determines whether there exists any identical objectthat is currently detected by the two detection sections. Thus, whiletaking into account the result of chronological matching, the detectiondevice also makes a momentary match based on two results of detectionthat are obtained from moment to moment. As a result, the detectiondevice is able to surely perform a match for any object that is detectedduring the current detection.

A related technique is described in the specification of U.S. Pat. No.7,417,580, the entire disclosure of which is incorporated herein byreference. In this publication, the image detection section isillustrated by way of a so-called stereo camera that includes twocameras. However, this technique is not limited thereto. In the casewhere the image detection section includes a single camera, detectedtargets may be subjected to an image recognition process or the like asappropriate, in order to obtain distance information and lateralposition information of the targets. Similarly, a laser sensor such as alaser scanner may be used as the image detection section.

In a third detection device, the two detection sections and matchingsection perform detection of targets and performs matches therebetweenat predetermined time intervals, and the results of such detection andthe results of such matching are chronologically stored to a storagemedium, e.g., memory. Then, based on a rate of change in the size of atarget in the image as detected by the image detection section, and on adistance to a target from the driver's vehicle and its rate of change(relative velocity with respect to the driver's vehicle) as detected bythe millimeter wave radar detection section, the matching sectiondetermines whether the target which has been detected by the imagedetection section and the target which has been detected by themillimeter wave radar detection section are an identical object.

When determining that these targets are an identical object, based onthe position of the target in the image as detected by the imagedetection section, and on the distance to the target from the driver'svehicle and/or its rate of change as detected by the millimeter waveradar detection section, the matching section predicts a possibility ofcollision with the vehicle.

A related technique is described in the specification of U.S. Pat. No.6,903,677, the entire disclosure of which is incorporated herein byreference.

As described above, in a fusion process of a millimeter wave radar andan imaging device such as a camera, an image which is obtained with thecamera or the like and radar information which is obtained with themillimeter wave radar are matched against each other. A millimeter waveradar incorporating the aforementioned array antenna according to anexample embodiment of the present disclosure can be constructed so as tohave a small size and high performance. Therefore, high performance anddownsizing, etc., can be achieved for the entire fusion processincluding the aforementioned matching process. This improves theaccuracy of target recognition, and enables safer travel control for thevehicle.

[Other Fusion Processes]

In a fusion process, various functions are realized based on a matchingprocess between an image which is obtained with a camera or the like andradar information which is obtained with the millimeter wave radardetection section. Examples of processing apparatuses that realizerepresentative functions of a fusion process will be described below.

Each of the following processing apparatuses is to be installed in avehicle, and at least includes: a millimeter wave radar detectionsection to transmit or receive electromagnetic waves in a predetermineddirection; an image acquisition section, such as a monocular camera,that has a field of view overlapping the field of view of the millimeterwave radar detection section; and a processing section which obtainsinformation therefrom to perform target detection and the like. Themillimeter wave radar detection section acquires radar information inits own field of view. The image acquisition section acquires imageinformation in its own field of view. A selected one, or selected two ormore of, an optical camera, LIDAR, an infrared radar, and an ultrasonicradar may be used as the image acquisition section. The processingsection can be implemented by a processing circuit which is connected tothe millimeter wave radar detection section and the image acquisitionsection. The following processing apparatuses differ from one anotherwith respect to the content of processing by this processing section.

In a first processing apparatus, the processing section extracts, froman image which is captured by the image acquisition section, a targetwhich is recognized to be the same as the target which is detected bythe millimeter wave radar detection section. In other words, a matchingprocess according to the aforementioned detection device is performed.Then, it acquires information of a right edge and a left edge of theextracted target image, and derives locus approximation lines, which arestraight lines or predetermined curved lines for approximating loci ofthe acquired right edge and the left edge, are derived for both edges.The edge which has a larger number of edges existing on the locusapproximation line is selected as a true edge of the target. The lateralposition of the target is derived on the basis of the position of theedge that has been selected as a true edge. This permits a furtherimprovement on the accuracy of detection of a lateral position of thetarget.

A related technique is described in the specification of U.S. Pat. No.8,610,620, the entire disclosure of which is incorporated herein byreference.

In a second processing apparatus, in determining the presence of atarget, the processing section alters a determination threshold to beused in checking for a target presence in radar information, on thebasis of image information. Thus, if a target image that may be anobstacle to vehicle travel has been confirmed with a camera or the like,or if the presence of a target has been estimated, etc., for example,the determination threshold for the target detection by the millimeterwave radar detection section can be optimized so that more accuratetarget information can be obtained. In other words, if the possibilityof the presence of an obstacle is high, the determination threshold isaltered so that this processing apparatus will surely be activated. Onthe other hand, if the possibility of the presence of an obstacle islow, the determination threshold is altered so that unwanted activationof this processing apparatus is prevented. This permits appropriateactivation of the system.

Furthermore in this case, based on radar information, the processingsection may designate a region of detection for the image information,and estimate a possibility of the presence of an obstacle on the basisof image information within this region. This makes for a more efficientdetection process.

A related technique is described in the specification of U.S. Pat. No.7,570,198, the entire disclosure of which is incorporated herein byreference.

In a third processing apparatus, the processing section performscombined displaying where images obtained from a plurality of differentimaging devices and a millimeter wave radar detection section and animage signal based on radar information are displayed on at least onedisplay device. In this displaying process, horizontal and verticalsynchronizing signals are synchronized between the plurality of imagingdevices and the millimeter wave radar detection section, and among theimage signals from these devices, selective switching to a desired imagesignal is possible within one horizontal scanning period or one verticalscanning period. This allows, on the basis of the horizontal andvertical synchronizing signals, images of a plurality of selected imagesignals to be displayed side by side; and, from the display device, acontrol signal for setting a control operation in the desired imagingdevice and the millimeter wave radar detection section is sent.

When a plurality of different display devices display respective imagesor the like, it is difficult to compare the respective images againstone another. Moreover, when display devices are provided separately fromthe third processing apparatus itself, there is poor operability for thedevice. The third processing apparatus would overcome such shortcomings.

A related technique is described in the specification of U.S. Pat. No.6,628,299 and the specification of U.S. Pat. No. 7,161,561, the entiredisclosure of each of which is incorporated herein by reference.

In a fourth processing apparatus, with respect to a target which isahead of a vehicle, the processing section instructs an imageacquisition section and a millimeter wave radar detection section toacquire an image and radar information containing that target. Fromwithin such image information, the processing section determines aregion in which the target is contained. Furthermore, the processingsection extracts radar information within this region, and detects adistance from the vehicle to the target and a relative velocity betweenthe vehicle and the target. Based on such information, the processingsection determines a possibility that the target will collide againstthe vehicle. This enables an early detection of a possible collisionwith a target.

A related technique is described in the specification of U.S. Pat. No.8,068,134, the entire disclosure of which is incorporated herein byreference.

In a fifth processing apparatus, based on radar information or through afusion process which is based on radar information and imageinformation, the processing section recognizes a target or two or moretargets ahead of the vehicle. The “target” encompasses any moving entitysuch as other vehicles or pedestrians, traveling lanes indicated bywhite lines on the road, road shoulders and any still objects (includinggutters, obstacles, etc.), traffic lights, pedestrian crossings, and thelike that may be there. The processing section may encompass a GPS(Global Positioning System) antenna. By using a GPS antenna, theposition of the driver's vehicle may be detected, and based on thisposition, a storage device (referred to as a map information databasedevice) that stores road map information may be searched in order toascertain a current position on the map. This current position on themap may be compared against a target or two or more targets that havebeen recognized based on radar information or the like, whereby thetraveling environment may be recognized. On this basis, the processingsection may extract any target that is estimated to hinder vehicletravel, find safer traveling information, and display it on a displaydevice, as necessary, to inform the driver.

A related technique is described in the specification of U.S. Pat. No.6,191,704, the entire disclosure of which is incorporated herein byreference.

The fifth processing apparatus may further include a data communicationdevice (having communication circuitry) that communicates with a mapinformation database device which is external to the vehicle. The datacommunication device may access the map information database device,with a period of e.g. once a week or once a month, to download thelatest map information therefrom. This allows the aforementionedprocessing to be performed with the latest map information.

Furthermore, the fifth processing apparatus may compare between thelatest map information that was acquired during the aforementionedvehicle travel and information that is recognized of a target or two ormore targets based on radar information, etc., in order to extracttarget information (hereinafter referred to as “map update information”)that is not included in the map information. Then, this map updateinformation may be transmitted to the map information database devicevia the data communication device. The map information database devicemay store this map update information in association with the mapinformation that is within the database, and update the current mapinformation itself, if necessary. In performing the update, respectivepieces of map update information that are obtained from a plurality ofvehicles may be compared against one another to check certainty of theupdate.

Note that this map update information may contain more detailedinformation than the map information which is carried by any currentlyavailable map information database device. For example, schematic shapesof roads may be known from commonly-available map information, but ittypically does not contain information such as the width of the roadshoulder, the width of the gutter that may be there, any newly occurringbumps or dents, shapes of buildings, and so on. Neither does it containheights of the roadway and the sidewalk, how a slope may connect to thesidewalk, etc. Based on conditions which are separately set, the mapinformation database device may store such detailed information(hereinafter referred to as “map update details information”) inassociation with the map information. Such map update detailsinformation provides a vehicle (including the driver's vehicle) withinformation which is more detailed than the original map information,thereby rending itself available for not only the purpose of ensuringsafe vehicle travel but also some other purposes. As used herein, a“vehicle (including the driver's vehicle)” may be e.g. an automobile, amotorcycle, a bicycle, or any autonomous vehicle to become available inthe future, e.g., an electric wheelchair. The map update detailsinformation is to be used when any such vehicle may travel.

(Recognition Via Neural Network)

Each of the first to fifth processing apparatuses may further include asophisticated apparatus of recognition. The sophisticated apparatus ofrecognition may be provided external to the vehicle. In that case, thevehicle may include a high-speed data communication device thatcommunicates with the sophisticated apparatus of recognition. Thesophisticated apparatus of recognition may be constructed from a neuralnetwork, which may encompass so-called deep learning and the like. Thisneural network may include a convolutional neural network (hereinafterreferred to as “CNN”), for example. A CNN, a neural network that hasproven successful in image recognition, is characterized by possessingone or more sets of two layers, namely, a convolutional layer and apooling layer.

There exists at least three kinds of information as follows, any ofwhich may be input to a convolutional layer in the processing apparatus:

(1) information that is based on radar information which is acquired bythe millimeter wave radar detection section;

(2) information that is based on specific image information which isacquired, based on radar information, by the image acquisition section;or

(3) fusion information that is based on radar information and imageinformation which is acquired by the image acquisition section, orinformation that is obtained based on such fusion information.

Based on information of any of the above kinds, or information based ona combination thereof, product-sum operations corresponding to aconvolutional layer are performed. The results are input to thesubsequent pooling layer, where data is selected according to apredetermined rule. In the case of max pooling where a maximum valueamong pixel values is chosen, for example, the rule may dictate that amaximum value be chosen for each split region in the convolutionallayer, this maximum value being regarded as the value of thecorresponding position in the pooling layer.

A sophisticated apparatus of recognition that is composed of a CNN mayinclude a single set of a convolutional layer and a pooling layer, or aplurality of such sets which are cascaded in series. This enablesaccurate recognition of a target, which is contained in the radarinformation and the image information, that may be around a vehicle.

Related techniques are described in the U.S. Pat. No. 8,861,842, thespecification of U.S. Pat. No. 9,286,524, and the specification of USPatent Application Publication No. 2016/0140424, the entire disclosureof each of which is incorporated herein by reference.

In a sixth processing apparatus, the processing section performsprocessing that is related to headlamp control of a vehicle. When avehicle travels in nighttime, the driver may check whether anothervehicle or a pedestrian exists ahead of the driver's vehicle, andcontrol a beam(s) from the headlamp(s) of the driver's vehicle toprevent the driver of the other vehicle or the pedestrian from beingdazzled by the headlamp(s) of the driver's vehicle. This sixthprocessing apparatus automatically controls the headlamp(s) of thedriver's vehicle by using radar information, or a combination of radarinformation and an image taken by a camera or the like.

Based on radar information, or through a fusion process based on radarinformation and image information, the processing section detects atarget that corresponds to a vehicle or pedestrian ahead of the vehicle.In this case, a vehicle ahead of a vehicle may encompass a precedingvehicle that is ahead, a vehicle or a motorcycle in the oncoming lane,and so on. When detecting any such target, the processing section issuesa command to lower the beam(s) of the headlamp(s). Upon receiving thiscommand, the control section (control circuit) which is internal to thevehicle may control the headlamp(s) to lower the beam(s) therefrom.

Related techniques are described in the specification of U.S. Pat. No.6,403,942, the specification of U.S. Pat. No. 6,611,610, thespecification of U.S. Pat. No. 8,543,277, the specification of U.S. Pat.No. 8,593,521, and the specification of U.S. Pat. No. 8,636,393, theentire disclosure of each of which is incorporated herein by reference.

According to the above-described processing by the millimeter wave radardetection section, and the above-described fusion process by themillimeter wave radar detection section and an imaging device such as acamera, the millimeter wave radar can be constructed so as to have asmall size and high performance, whereby high performance anddownsizing, etc., can be achieved for the radar processing or the entirefusion process. This improves the accuracy of target recognition, andenables safer travel control for the vehicle.

Application Example 2: Various Monitoring Systems (Natural Elements,Buildings, Roads, Watch, Security)

A millimeter wave radar (radar system) incorporating an array antennaaccording to an example embodiment of the present disclosure also has awide range of applications in the fields of monitoring, which mayencompass natural elements, weather, buildings, security, nursing care,and the like. In a monitoring system in this context, a monitoringapparatus that includes the millimeter wave radar may be installed e.g.at a fixed position, in order to perpetually monitor a subject(s) ofmonitoring. Regarding the given subject(s) of monitoring, the millimeterwave radar has its resolution of detection adjusted and set to anoptimum value.

A millimeter wave radar incorporating an array antenna according to anexample embodiment of the present disclosure is capable of detectionwith a radio frequency electromagnetic wave exceeding e.g. 100 GHz. Asfor the modulation band in those schemes which are used in radarrecognition, e.g., the FMCW method, the millimeter wave radar currentlyachieves a wide band exceeding 4 GHz, which supports the aforementionedUltra Wide Band (UWB). Note that the modulation band is related to therange resolution. In a conventional patch antenna, the modulation bandwas up to about 600 MHz, thus resulting in a range resolution of 25 cm.On the other hand, a millimeter wave radar associated with the presentarray antenna has a range resolution of 3.75 cm, indicative of aperformance which rivals the range resolution of conventional LIDAR.Whereas an optical sensor such as LIDAR is unable to detect a target innighttime or bad weather as mentioned above, a millimeter wave radar isalways capable of detection, regardless of daytime or nighttime andirrespective of weather. As a result, a millimeter wave radar associatedwith the present array antenna is available for a variety ofapplications which were not possible with a millimeter wave radarincorporating any conventional patch antenna.

FIG. 51 is a diagram showing an exemplary construction for a monitoringsystem 1500 based on millimeter wave radar. The monitoring system 1500based on millimeter wave radar at least includes a sensor section 1010and a main section 1100. The sensor section 1010 at least includes anantenna 1011 which is aimed at the subject of monitoring 1015, amillimeter wave radar detection section 1012 which detects a targetbased on a transmitted or received electromagnetic wave, and acommunication section (communication circuit) 1013 which transmitsdetected radar information. The main section 1100 at least includes acommunication section (communication circuit) 1103 which receives radarinformation, a processing section (processing circuit) 1101 whichperforms predetermined processing based on the received radarinformation, and a data storage section (storage medium) 1102 in whichpast radar information and other information that is needed for thepredetermined processing, etc., are stored. Telecommunication lines 1300exist between the sensor section 1010 and the main section 1100, viawhich transmission and reception of information and commands occurbetween them. As used herein, the telecommunication lines may encompassany of a general-purpose communications network such as the Internet, amobile communications network, dedicated telecommunication lines, and soon, for example. Note that the present monitoring system 1500 may bearranged so that the sensor section 1010 and the main section 1100 aredirectly connected, rather than via telecommunication lines. In additionto the millimeter wave radar, the sensor section 1010 may also includean optical sensor such as a camera. This will permit target recognitionthrough a fusion process which is based on radar information and imageinformation from the camera or the like, thus enabling a moresophisticated detection of the subject of monitoring 1015 or the like.

Hereinafter, examples of monitoring systems embodying these applicationswill be specifically described.

[Natural Element Monitoring System]

A first monitoring system is a system that monitors natural elements(hereinafter referred to as a “natural element monitoring system”). Withreference to FIG. 51, this natural element monitoring system will bedescribed. Subjects of monitoring 1015 of the natural element monitoringsystem 1500 may be, for example, a river, the sea surface, a mountain, avolcano, the ground surface, or the like. For example, when a river isthe subject of monitoring 1015, the sensor section 1010 being secured toa fixed position perpetually monitors the water surface of the river1015. This water surface information is perpetually transmitted to aprocessing section 1101 in the main section 1100. Then, if the watersurface reaches a certain height or above, the processing section 1101informs a distinct system 1200 which separately exists from themonitoring system (e.g., a weather observation monitoring system), viathe telecommunication lines 1300. Alternatively, the processing section1101 may send information to a system (not shown) which manages thewater gate, whereby the system if instructed to automatically close awater gate, etc. (not shown) which is provided at the river 1015.

The natural element monitoring system 1500 is able to monitor aplurality of sensor sections 1010, 1020, etc., with the single mainsection 1100. When the plurality of sensor sections are distributed overa certain area, the water levels of rivers in that area can be graspedsimultaneously. This allows to make an assessment as to how the rainfallin this area may affect the water levels of the rivers, possibly leadingto disasters such as floods. Information concerning this can be conveyedto the distinct system 1200 (e.g., a weather observation monitoringsystem) via the telecommunication lines 1300. Thus, the distinct system1200 (e.g., a weather observation monitoring system) is able to utilizethe conveyed information for weather observation or disaster predictionin a wider area.

The natural element monitoring system 1500 is also similarly applicableto any natural element other than a river. For example, the subject ofmonitoring of a monitoring system that monitors tsunamis or storm surgesis the sea surface level. It is also possible to automatically open orclose the water gate of a seawall in response to a rise in the seasurface level. Alternatively, the subject of monitoring of a monitoringsystem that monitors landslides to be caused by rainfall, earthquakes,or the like may be the ground surface of a mountainous area, etc.

[Traffic Monitoring System]

A second monitoring system is a system that monitors traffic(hereinafter referred to as a “traffic monitoring system”). The subjectof monitoring of this traffic monitoring system may be, for example, arailroad crossing, a specific railroad, an airport runway, a roadintersection, a specific road, a parking lot, etc.

For example, when the subject of monitoring is a railroad crossing, thesensor section 1010 is placed at a position where the inside of thecrossing can be monitored. In this case, in addition to the millimeterwave radar, the sensor section 1010 may also include an optical sensorsuch as a camera, which will allow a target (subject of monitoring) tobe detected from more perspectives, through a fusion process based onradar information and image information. The target information which isobtained with the sensor section 1010 is sent to the main section 1100via the telecommunication lines 1300. The main section 1100 collectsother information (e.g., train schedule information) that may be neededin a more sophisticated recognition process or control, and issuesnecessary control instructions or the like based thereon. As usedherein, a necessary control instruction may be, for example, aninstruction to stop a train when a person, a vehicle, etc. is foundinside the crossing when it is closed.

If the subject of monitoring is a runway at an airport, for example, aplurality of sensor sections 1010, 1020, etc., may be placed along therunway so as to set the runway to a predetermined resolution, e.g., aresolution that allows any foreign object on the runway that is 5 cm by5 cm or larger to be detected. The monitoring system 1500 perpetuallymonitors the runway, regardless of daytime or nighttime and irrespectiveof weather. This function is enabled by the very ability of themillimeter wave radar according to an example embodiment of the presentdisclosure to support UWB. Moreover, since the present millimeter waveradar device can be embodied with a small size, a high resolution, and alow cost, it provides a realistic solution for covering the entirerunway surface from end to end. In this case, the main section 1100keeps the plurality of sensor sections 1010, 1020, etc., underintegrated management. If a foreign object is found on the runway, themain section 1100 transmits information concerning the position and sizeof the foreign object to an air-traffic control system (not shown). Uponreceiving this, the air-traffic control system temporarily prohibitstakeoff and landing on that runway. In the meantime, the main section1100 transmits information concerning the position and size of theforeign object to a separately-provided vehicle, which automaticallycleans the runway surface, etc., for example. Upon receive this, thecleaning vehicle may autonomously move to the position where the foreignobject exists, and automatically remove the foreign object. Once removalof the foreign object is completed, the cleaning vehicle transmitsinformation of the completion to the main section 1100. Then, the mainsection 1100 again confirms that the sensor section 1010 or the likewhich has detected the foreign object now reports that “no foreignobject exists” and that it is safe now, and informs the air-trafficcontrol system of this. Upon receiving this, the air-traffic controlsystem may lift the prohibition of takeoff and landing from the runway.

Furthermore, in the case where the subject of monitoring is a parkinglot, for example, it may be possible to automatically recognize whichposition in the parking lot is currently vacant. A related technique isdescribed in the specification of U.S. Pat. No. 6,943,726, the entiredisclosure of which is incorporated herein by reference.

[Security Monitoring System]

A third monitoring system is a system that monitors a trespasser into apiece of private land or a house (hereinafter referred to as a “securitymonitoring system”). The subject of monitoring of this securitymonitoring system may be, for example, a specific region within a pieceof private land or a house, etc.

For example, if the subject of monitoring is a piece of private land,the sensor section(s) 1010 may be placed at one position, or two or morepositions where the sensor section(s) 1010 is able to monitor it. Inthis case, in addition to the millimeter wave radar, the sensorsection(s) 1010 may also include an optical sensor such as a camera,which will allow a target (subject of monitoring) to be detected frommore perspectives, through a fusion process based on radar informationand image information. The target information which was obtained by thesensor section 1010(s) is sent to the main section 1100 via thetelecommunication lines 1300. The main section 1100 collects otherinformation (e.g., reference data or the like needed to accuratelyrecognize whether the trespasser is a person or an animal such as a dogor a bird) that may be needed in a more sophisticated recognitionprocess or control, and issues necessary control instructions or thelike based thereon. As used herein, a necessary control instruction maybe, for example, an instruction to sound an alarm or activate lightingthat is installed in the premises, and also an instruction to directlyreport to a person in charge of the premises via mobiletelecommunication lines or the like, etc. The processing section 1101 inthe main section 1100 may allow an internalized, sophisticated apparatusof recognition (that adopts deep learning or a like technique) torecognize the detected target. Alternatively, such a sophisticatedapparatus of recognition may be provided externally, in which case thesophisticated apparatus of recognition may be connected via thetelecommunication lines 1300.

A related technique is described in the specification of U.S. Pat. No.7,425,983, the entire disclosure of which is incorporated herein byreference.

Another example embodiment of such a security monitoring system may be ahuman monitoring system to be installed at a boarding gate at anairport, a station wicket, an entrance of a building, or the like. Thesubject of monitoring of such a human monitoring system may be, forexample, a boarding gate at an airport, a station wicket, an entrance ofa building, or the like.

If the subject of monitoring is a boarding gate at an airport, thesensor section(s) 1010 may be installed in a machine for checkingpersonal belongings at the boarding gate, for example. In this case,there may be two checking methods as follows. In a first method, themillimeter wave radar transmits an electromagnetic wave, and receivesthe electromagnetic wave as it reflects off a passenger (which is thesubject of monitoring), thereby checking personal belongings or the likeof the passenger. In a second method, a weak millimeter wave which isradiated from the passenger's own body is received by the antenna, thuschecking for any foreign object that the passenger may be hiding. In thelatter method, the millimeter wave radar preferably has a function ofscanning the received millimeter wave. This scanning function may beimplemented by using digital beam forming, or through a mechanicalscanning operation. Note that the processing by the main section 1100may utilize a communication process and a recognition process similar tothose in the above-described examples.

[Building Inspection System (Non-Destructive Inspection)]

A fourth monitoring system is a system that monitors or checks theconcrete material of a road, a railroad overpass, a building, etc., orthe interior of a road or the ground, etc., (hereinafter referred to asa “building inspection system”). The subject of monitoring of thisbuilding inspection system may be, for example, the interior of theconcrete material of an overpass or a building, etc., or the interior ofa road or the ground, etc.

For example, if the subject of monitoring is the interior of a concretebuilding, the sensor section 1010 is structured so that the antenna 1011can make scan motions along the surface of a concrete building. As usedherein, “scan motions” may be implemented manually, or a stationary railfor the scan motion may be separately provided, upon which to cause themovement by using driving power from an electric motor or the like. Inthe case where the subject of monitoring is a road or the ground, theantenna 1011 may be installed face-down on a vehicle or the like, andthe vehicle may be allowed to travel at a constant velocity, thuscreating a “scan motion”. The electromagnetic wave to be used by thesensor section 1010 may be a millimeter wave in e.g. the so-calledterahertz region, exceeding 100 GHz. As described earlier, even with anelectromagnetic wave over e.g. 100 GHz, an array antenna according to anexample embodiment of the present disclosure can be adapted to havesmaller losses than do conventional patch antennas or the like. Anelectromagnetic wave of a higher frequency is able to permeate deeperinto the subject of checking, such as concrete, thereby realizing a moreaccurate non-destructive inspection. Note that the processing by themain section 1100 may also utilize a communication process and arecognition process similar to those in the other monitoring systemsdescribed above.

A related technique is described in the specification of U.S. Pat. No.6,661,367, the entire disclosure of which is incorporated herein byreference.

[Human Monitoring System]

A fifth monitoring system is a system that watches over a person who issubject to nursing care (hereinafter referred to as a “human watchsystem”). The subject of monitoring of this human watch system may be,for example, a person under nursing care or a patient in a hospital,etc.

For example, if the subject of monitoring is a person under nursing carewithin a room of a nursing care facility, the sensor section(s) 1010 isplaced at one position, or two or more positions inside the room wherethe sensor section(s) 1010 is able to monitor the entirety of the insideof the room. In this case, in addition to the millimeter wave radar, thesensor section 1010 may also include an optical sensor such as a camera.In this case, the subject of monitoring can be monitored from moreperspectives, through a fusion process based on radar information andimage information. On the other hand, when the subject of monitoring isa person, from the standpoint of privacy protection, monitoring with acamera or the like may not be appropriate. Therefore, sensor selectionsmust be made while taking this aspect into consideration. Note thattarget detection by the millimeter wave radar will allow a person, whois the subject of monitoring, to be captured not by his or her image,but by a signal (which is, as it were, a shadow of the person).Therefore, the millimeter wave radar may be considered as a desirablesensor from the standpoint of privacy protection.

Information of the person under nursing care which has been obtained bythe sensor section(s) 1010 is sent to the main section 1100 via thetelecommunication lines 1300. The main section 1100 collects otherinformation (e.g., reference data or the like needed to accuratelyrecognize target information of the person under nursing care) that maybe needed in a more sophisticated recognition process or control, andissues necessary control instructions or the like based thereon. As usedherein, a necessary control instruction may be, for example, aninstruction to directly report a person in charge based on the result ofdetection, etc. The processing section 1101 in the main section 1100 mayallow an internalized, sophisticated apparatus of recognition (thatadopts deep learning or a like technique) to recognize the detectedtarget. Alternatively, such a sophisticated apparatus of recognition maybe provided externally, in which case the sophisticated apparatus ofrecognition may be connected via the telecommunication lines 1300.

In the case where a person is the subject of monitoring of themillimeter wave radar, at least the two following functions may beadded.

A first function is a function of monitoring the heart rate and/or therespiratory rate. In the case of a millimeter wave radar, anelectromagnetic wave is able to see through the clothes to detect theposition and motions of the skin surface of a person's body. First, theprocessing section 1101 detects a person who is the subject ofmonitoring and an outer shape thereof. Next, in the case of detecting aheart rate, for example, a position on the body surface where theheartbeat motions are easy to detect may be identified, and the motionsthere may be chronologically detected. This allows a heart rate perminute to be detected, for example. The same is also true when detectinga respiratory rate. By using this function, the health status of aperson under nursing care can be perpetually checked, thus enabling ahigher-quality watch over a person under nursing care.

A second function is a function of fall detection. A person undernursing care such as an elderly person may fall from time to time, dueto weakened legs and feet. When a person falls, the velocity oracceleration of a specific site of the person's body, e.g., the head,will reach a certain level or greater. When the subject of monitoring ofthe millimeter wave radar is a person, the relative velocity oracceleration of the target of interest can be perpetually detected.Therefore, by identifying the head as the subject of monitoring, forexample, and chronologically detecting its relative velocity oracceleration, a fall can be recognized when a velocity of a certainvalue or greater is detected. When recognizing a fall, the processingsection 1101 can issue an instruction or the like corresponding topertinent nursing care assistance, for example.

Note that the sensor section(s) 1010 is secured to a fixed position(s)in the above-described monitoring system or the like. However, thesensor section(s) 1010 can also be installed on a moving entity, e.g., arobot, a vehicle, a flying object such as a drone. As used herein, thevehicle or the like may encompass not only an automobile, but also asmaller sized moving entity such as an electric wheelchair, for example.In this case, this moving entity may include an internal GPS unit whichallows its own current position to be always confirmed. In addition,this moving entity may also have a function of further improving theaccuracy of its own current position by using map information and themap update information which has been described with respect to theaforementioned fifth processing apparatus.

Furthermore, in any device or system that is similar to theabove-described first to third detection devices, first to sixthprocessing apparatuses, first to fifth monitoring systems, etc., a likeconstruction may be adopted to utilize an array antenna or a millimeterwave radar according to an example embodiment of the present disclosure.

Application Example 3: Communication System [First Example ofCommunication System]

The waveguide device and antenna device (array antenna) according to thepresent disclosure can be used for the transmitter and/or receiver withwhich a communication system (telecommunication system) is constructed.The waveguide device and antenna device according to the presentdisclosure are composed of layered conductive members, and therefore areable to keep the transmitter and/or receiver size smaller than in thecase of using a hollow waveguide. Moreover, there is no need fordielectric, and thus the dielectric loss of electromagnetic waves can bekept smaller than in the case of using a microstrip line. Therefore, acommunication system including a small and highly efficient transmitterand/or receiver can be constructed.

Such a communication system may be an analog type communication systemwhich transmits or receives an analog signal that is directly modulated.However, a digital communication system may be adopted in order toconstruct a more flexible and higher-performance communication system.

Hereinafter, with reference to FIG. 52, a digital communication system800A in which a waveguide device and an antenna device according to anexample embodiment of the present disclosure are used will be described.

FIG. 52 is a block diagram showing a construction for the digitalcommunication system 800A. The communication system 800A includes atransmitter 810A and a receiver 820A. The transmitter 810A includes ananalog to digital (A/D) converter 812, an encoder 813, a modulator 814,and a transmission antenna 815. The receiver 820A includes a receptionantenna 825, a demodulator 824, a decoder 823, and a digital to analog(D/A) converter 822. The at least one of the transmission antenna 815and the reception antenna 825 may be implemented by using an arrayantenna according to an example embodiment of the present disclosure. Inthis exemplary application, the circuitry including the modulator 814,the encoder 813, the A/D converter 812, and so on, which are connectedto the transmission antenna 815, is referred to as the transmissioncircuit. The circuitry including the demodulator 824, the decoder 823,the D/A converter 822, and so on, which are connected to the receptionantenna 825, is referred to as the reception circuit. The transmissioncircuit and the reception circuit may be collectively referred to as thecommunication circuit.

With the analog to digital (A/D) converter 812, the transmitter 810Aconverts an analog signal which is received from the signal source 811to a digital signal. Next, the digital signal is encoded by the encoder813. As used herein, “encoding” means altering the digital signal to betransmitted into a format which is suitable for communication. Examplesof such encoding include CDM (Code-Division Multiplexing) and the like.Moreover, any conversion for effecting TDM (Time-Division Multiplexing)or FDM (Frequency Division Multiplexing), or OFDM (Orthogonal FrequencyDivision Multiplexing) is also an example of encoding. The encodedsignal is converted by the modulator 814 into a radio frequency signal,so as to be transmitted from the transmission antenna 815.

In the field of communications, a wave representing a signal to besuperposed on a carrier wave may be referred to as a “signal wave”;however, the term “signal wave” as used in the present specificationdoes not carry that definition. A “signal wave” as referred to in thepresent specification is broadly meant to be any electromagnetic wave topropagate in a waveguide, or any electromagnetic wave fortransmission/reception via an antenna element.

The receiver 820A restores the radio frequency signal that has beenreceived by the reception antenna 825 to a lowfrequency signal at thedemodulator 824, and to a digital signal at the decoder 823. The decodeddigital signal is restored to an analog signal by the digital to analog(D/A) converter 822, and is sent to a data sink (data receiver) 821.Through the above processes, a sequence of transmission and receptionprocesses is completed.

When the communicating agent is a digital appliance such as a computer,analog to digital conversion of the transmission signal and digital toanalog conversion of the reception signal are not needed in theaforementioned processes. Thus, the analog to digital converter 812 andthe digital to analog converter 822 in FIG. 52 may be omitted. A systemof such construction is also encompassed within a digital communicationsystem.

In a digital communication system, in order to ensure signal intensityor expand channel capacity, various methods may be adopted. Many suchmethods are also effective in a communication system which utilizesradio waves of the millimeter wave band or the terahertz band.

Radio waves in the millimeter wave band or the terahertz band havehigher straightness than do radio waves of lower frequencies, andundergoes less diffraction, i.e., bending around into the shadow side ofan obstacle. Therefore, it is not uncommon for a receiver to fail todirectly receive a radio wave that has been transmitted from atransmitter. Even in such situations, reflected waves may often bereceived, but a reflected wave of a radio wave signal is often poorer inquality than is the direct wave, thus making stable reception moredifficult. Furthermore, a plurality of reflected waves may arrivethrough different paths. In that case, the reception waves withdifferent path lengths might differ in phase from one another, thuscausing multi-path fading.

As a technique for improving such situations, a so-called antennadiversity technique may be used. In this technique, at least one of thetransmitter and the receiver includes a plurality of antennas. If theplurality of antennas are parted by distances which differ from oneanother by at least about the wavelength, the resulting states of thereception waves will be different. Accordingly, the antenna that iscapable of transmission/reception with the highest quality among all isselectively used, thereby enhancing the reliability of communication.Alternatively, signals which are obtained from more than one antenna maybe merged for an improved signal quality.

In the communication system 800A shown in FIG. 52, for example, thereceiver 820A may include a plurality of reception antennas 825. In thiscase, a switcher exists between the plurality of reception antennas 825and the demodulator 824. Through the switcher, the receiver 820Aconnects the antenna that provides the highest-quality signal among theplurality of reception antennas 825 to the demodulator 824. In thiscase, the transmitter 810A may also include a plurality of transmissionantennas 815.

[Second Example of Communication System]

FIG. 53 is a block diagram showing an example of a communication system800B including a transmitter 810B which is capable of varying theradiation pattern of radio waves. In this exemplary application, thereceiver is identical to the receiver 820A shown in FIG. 52; for thisreason, the receiver is omitted from illustration in FIG. 53. Inaddition to the construction of the transmitter 810A, the transmitter810B also includes an antenna array 815 b, which includes a plurality ofantenna elements 8151. The antenna array 815 b may be an array antennaaccording to an example embodiment of the present disclosure. Thetransmitter 810B further includes a plurality of phase shifters (PS) 816which are respectively connected between the modulator 814 and theplurality of antenna elements 8151. In the transmitter 810B, an outputof the modulator 814 is sent to the plurality of phase shifters 816,where phase differences are imparted and the resultant signals are ledto the plurality of antenna elements 8151. In the case where theplurality of antenna elements 8151 are disposed at equal intervals, if aradio frequency signal whose phase differs by a certain amount withrespect to an adjacent antenna element is fed to each antenna element8151, a main lobe 817 of the antenna array 815 b will be oriented in anazimuth which is inclined from the front, this inclination being inaccordance with the phase difference. This method may be referred to asbeam forming.

The azimuth of the main lobe 817 may be altered by allowing therespective phase shifters 816 to impart varying phase differences. Thismethod may be referred to as beam steering. By finding phase differencesthat are conducive to the best transmission/reception state, thereliability of communication can be enhanced. Although the example hereillustrates a case where the phase difference to be imparted by thephase shifters 816 is constant between any adjacent antenna elements8151, this is not limiting. Moreover, phase differences may be impartedso that the radio wave will be radiated in an azimuth which allows notonly the direct wave but also reflected waves to reach the receiver.

A method called null steering can also be used in the transmitter 810B.This is a method where phase differences are adjusted to create a statewhere the radio wave is radiated in no specific direction. By performingnull steering, it becomes possible to restrain radio waves from beingradiated toward any other receiver to which transmission of the radiowave is not intended. This can avoid interference. Although a very broadfrequency band is available to digital communication utilizingmillimeter waves or terahertz waves, it is nonetheless preferable tomake as efficient a use of the bandwidth as possible. By using nullsteering, plural instances of transmission/reception can be performedwithin the same band, whereby efficiency of utility of the bandwidth canbe enhanced. A method which enhances the efficiency of utility of thebandwidth by using techniques such as beam forming, beam steering, andnull steering may sometimes be referred to as SDMA (Spatial DivisionMultiple Access).

[Third Example of Communication System]

In order to increase the channel capacity in a specific frequency band,a method called MIMO (Multiple-Input and MultipleOutput) may be adopted.Under MIMO, a plurality of transmission antennas and a plurality ofreception antennas are used. A radio wave is radiated from each of theplurality of transmission antennas. In one example, respectivelydifferent signals may be superposed on the radio waves to be radiated.Each of the plurality of reception antennas receives all of thetransmitted plurality of radio waves. However, since different receptionantennas will receive radio waves that arrive through different paths,differences will occur among the phases of the received radio waves. Byutilizing these differences, it is possible to, at the receiver side,separate the plurality of signals which were contained in the pluralityof radio waves.

The waveguide device and antenna device according to the presentdisclosure can also be used in a communication system which utilizesMIMO. Hereinafter, an example such a communication system will bedescribed.

FIG. 54 is a block diagram showing an example of a communication system800C implementing a MIMO function. In the communication system 800C, atransmitter 830 includes an encoder 832, a TX-MIMO processor 833, andtwo transmission antennas 8351 and 8352. A receiver 840 includes tworeception antennas 8451 and 8452, an RX-MIMO processor 843, and adecoder 842. Note that the number of transmission antennas and thenumber of reception antennas may each be greater than two. Herein, forease of explanation, an example where there are two antennas of eachkind will be illustrated. In general, the channel capacity of an MIMOcommunication system will increase in proportion to the number ofwhichever is the fewer between the transmission antennas and thereception antennas.

Having received a signal from the data signal source 831, thetransmitter 830 encodes the signal at the encoder 832 so that the signalis ready for transmission. The encoded signal is distributed by theTX-MIMO processor 833 between the two transmission antennas 8351 and8352.

In a processing method according to one example of the MIMO method, theTX-MIMO processor 833 splits a sequence of encoded signals into two,i.e., as many as there are transmission antennas 8352, and sends them inparallel to the transmission antennas 8351 and 8352. The transmissionantennas 8351 and 8352 respectively radiate radio waves containinginformation of the split signal sequences. When there are N transmissionantennas, the signal sequence is split into N. The radiated radio wavesare simultaneously received by the two reception antennas 8451 and 8452.In other words, in the radio waves which are received by each of thereception antennas 8451 and 8452, the two signals which were split atthe time of transmission are mixedly contained. Separation between thesemixed signals is achieved by the RX-MIMO processor 843.

The two mixed signals can be separated by paying attention to the phasedifferences between the radio waves, for example. A phase differencebetween two radio waves of the case where the radio waves which havearrived from the transmission antenna 8351 are received by the receptionantennas 8451 and 8452 is different from a phase difference between tworadio waves of the case where the radio waves which have arrived fromthe transmission antenna 8352 are received by the reception antennas8451 and 8452. That is, the phase difference between reception antennasdiffers depending on the path of transmission/reception. Moreover,unless the spatial relationship between a transmission antenna and areception antenna is changed, the phase difference therebetween remainsunchanged. Therefore, based on correlation between reception signalsreceived by the two reception antennas, as shifted by a phase differencewhich is determined by the path of transmission/reception, it ispossible to extract any signal that is received through that path oftransmission/reception. The RX-MIMO processor 843 may separate the twosignal sequences from the reception signal e.g. by this method, thusrestoring the signal sequence before the split. The restored signalsequence still remains encoded, and therefore is sent to the decoder 842so as to be restored to the original signal there. The restored signalis sent to the data sink 841.

Although the MIMO communication system 800C in this example transmits orreceives a digital signal, an MIMO communication system which transmitsor receives an analog signal can also be realized. In that case, inaddition to the construction of FIG. 54, an analog to digital converterand a digital to analog converter as have been described with referenceto FIG. 52 are provided. Note that the information to be used indistinguishing between signals from different transmission antennas isnot limited to phase difference information. Generally speaking, for adifferent combination of a transmission antenna and a reception antenna,the received radio wave may differ not only in terms of phase, but alsoin scatter, fading, and other conditions. These are collectivelyreferred to as CSI (Channel State Information). CSI may be utilized indistinguishing between different paths of transmission/reception in asystem utilizing MIMO.

Note that it is not an essential requirement that the plurality oftransmission antennas radiate transmission waves containing respectivelyindependent signals. So long as separation is possible at the receptionantenna side, each transmission antenna may radiate a radio wavecontaining a plurality of signals. Moreover, beam forming may beperformed at the transmission antenna side, while a transmission wavecontaining a single signal, as a synthetic wave of the radio waves fromthe respective transmission antennas, may be formed at the receptionantenna. In this case, too, each transmission antenna is adapted so asto radiate a radio wave containing a plurality of signals.

In this third example, too, as in the first and second examples, variousmethods such as CDM, FDM, TDM, and OFDM may be used as a method ofsignal encoding.

In a communication system, a circuit board that implements an integratedcircuit (referred to as a signal processing circuit or a communicationcircuit) for processing signals may be stacked as a layer on thewaveguide device and antenna device according to an example embodimentof the present disclosure. Since the waveguide device and antenna deviceaccording to an example embodiment of the present disclosure isstructured so that plate-like conductive members are layered therein, itis easy to further stack a circuit board thereupon. By adopting such anarrangement, a transmitter and a receiver which are smaller in volumethan in the case where a hollow waveguide or the like is employed can berealized.

In the first to third examples of the communication system as describedabove, each element of a transmitter or a receiver, e.g., an analog todigital converter, a digital to analog converter, an encoder, a decoder,a modulator, a demodulator, a TX-MIMO processor, or an RX-MIMOprocessor, is illustrated as one independent element in FIGS. 52, 53,and 54; however, these do not need to be discrete. For example, all ofthese elements may be realized by a single integrated circuit.Alternatively, some of these elements may be combined so as to berealized by a single integrated circuit. Either case qualifies as anexample embodiment of the present invention so long as the functionswhich have been described in the present disclosure are realizedthereby.

A waveguide device and an antenna device according to the presentdisclosure is usable in any technological field that makes use of anantenna. For example, they are available to various applications wheretransmission/reception of electromagnetic waves of the gigahertz band orthe terahertz band is performed. In particular, they may be used inonboard radar systems, various types of monitoring systems, indoorpositioning systems, wireless communication systems, etc., wheredownsizing is desired.

While example embodiments of the present disclosure have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present disclosure. The scope of the presentdisclosure, therefore, is to be determined solely by the followingclaims.

What is claimed is:
 1. A waveguide device comprising: an electricalconductor including an electrically conductive surface; a waveguideincluding an electrically-conductive waveguide surface opposed to theelectrically conductive surface, and extending alongside theelectrically conductive surface; and an artificial magnetic conductorextending on two sides of the waveguide; wherein the waveguide includesa first portion extending in one direction and at least two branchesextending from one end of the first portion, the at least two branchesincluding a second portion and a third portion that extend in mutuallydifferent directions; the waveguide defined by the electricallyconductive surface, the waveguide surface, and the artificial magneticconductor includes an enlarged gap portion at which a gap between theelectrically conductive surface and the waveguide surface is locallyenlarged; a size of the gap between the electrically conductive surfaceand the waveguide surface is greater at the enlarged gap portion than atany site on the waveguide that is adjacent to the enlarged gap portion,and is smaller than a distance between the electrically conductivesurface and a root of the waveguide; and at least a portion of ajunction at which the first portion is joined with the at least twobranches of the waveguide overlaps the enlarged gap portion, as seenthrough in a direction perpendicular to the electrically conductivesurface.
 2. The waveguide device of claim 1, wherein a side-surfacejunction between a side surface of the first portion and a side surfaceof at least one of the second and third portions is curved.
 3. Thewaveguide device of claim 1, wherein, as seen through in a directionperpendicular or substantially perpendicular to the electricallyconductive surface, an entirety of the junction is located inside theenlarged gap portion.
 4. The waveguide device of claim 1, wherein aside-surface junction between a side surface of the first portion and aside surface of at least one of the second and third portions is curved;and as seen through in a direction perpendicular or substantiallyperpendicular to the electrically conductive surface, the entirejunction is located inside the enlarged gap portion.
 5. The waveguidedevice of claim 1, wherein the at least two branches include no morethan two branches; and as seen through in a direction perpendicular orsubstantially perpendicular to the electrically conductive surface, anouter edge of the enlarged gap portion reaches an edge of the twobranches or the junction on an opposite side from the first portion. 6.The waveguide device of claim 1, wherein a side-surface junction betweena side surface of the first portion and a side surface of at least oneof the second and third portions is curved; the at least two branchesinclude no more than two branches; and as seen through in a directionperpendicular or substantially perpendicular to the electricallyconductive surface, an outer edge of the enlarged gap portion reaches anedge of the two branches or the junction on an opposite side from thefirst portion.
 7. The waveguide device of claim 1, wherein a dimensionof the enlarged gap portion along a width direction of the first portionis greater than a width of the first portion.
 8. The waveguide device ofclaim 1, wherein a side-surface junction between a side surface of thefirst portion and a side surface of at least one of the second and thirdportions is curved; and a dimension of the enlarged gap portion along awidth direction of the first portion is greater than a width of thefirst portion.
 9. The waveguide device of claim 1, wherein at least oneof the waveguide surface and the electrically conductive surfaceincludes a recess at the enlarged gap portion; and a dimension of therecess as measured along a width direction of the first portion isgreater than a depth of a bottom of the recess relative to the waveguidesurface or the electrically conductive surface around the recess. 10.The waveguide device of claim 1, wherein at least one of the waveguidesurface and the electrically conductive surface includes a recess at theenlarged gap portion; a dimension of the recess as measured along awidth direction of the first portion is greater than a depth of a bottomof the recess relative to the waveguide surface or the electricallyconductive surface around the recess; and a side-surface junctionbetween a side surface of the first portion and a side surface of atleast one of the second and third portions is curved.
 11. The waveguidedevice of claim 1, wherein the waveguide surface includes a first recessat the enlarged gap portion; the electrically conductive surfaceincludes a second recess at the enlarged gap portion; and a dimension ofthe first recess and a dimension of the second recess as measured alonga width direction of the first portion are each greater than a sum of adepth of a bottom of the first recess relative to any site on thewaveguide surface that is around the first recess and a depth of abottom of the second recess relative to any site on the electricallyconductive surface that is around the second recess.
 12. The waveguidedevice of claim 1, wherein the at least two branches further include afourth portion which extends in a different direction from directions inwhich the second and third portions extend.
 13. The waveguide device ofclaim 1, wherein at the junction where the first to third portions arejoined with one another, the waveguide includes a first depression on aside surface opposite to the first portion, the first depressionreaching the waveguide surface; and as viewed in a directionperpendicular or substantially perpendicular to the waveguide surface,the first depression overlaps the enlarged gap portion.
 14. Thewaveguide device of claim 1, wherein at the junction where the first tothird portions are joined with one another, the waveguide includes afirst depression on a side surface opposite to the first portion, thefirst depression reaching the waveguide surface; as viewed in adirection perpendicular or substantially perpendicular to the waveguidesurface, the first depression overlaps the enlarged gap portion; and aside-surface junction between a side surface of the first portion and aside surface of at least one of the second and third portions is curved.15. The waveguide device of claim 1, wherein at the junction where thefirst to third portions are joined with one another, the waveguideincludes a first depression on a side surface opposite to the firstportion, the first depression reaching the waveguide surface; as viewedin a direction perpendicular or substantially perpendicular to thewaveguide surface, the first depression overlaps the enlarged gapportion; the at least two branches include no more than two branches;and as seen through in a direction perpendicular to the electricallyconductive surface, an outer edge of the enlarged gap portion reaches anedge of the two branches or the junction on an opposite side from thefirst portion.
 16. The waveguide device of claim 1, wherein the secondportion includes a second depression on a side surface connecting to oneside surface of the first portion, the second depression reaching thewaveguide surface; the third portion includes a third depression on aside surface connecting to another side surface of the first portion,the third depression reaching the waveguide surface; as viewed in adirection perpendicular or substantially perpendicular to the waveguidesurface, a distance from a point of intersection between the sidesurface of the first portion and the side surface of the second portionto a center of the second depression is shorter than a length of thesecond depression along the direction that the second portion extends,and a distance from a point of intersection between the other sidesurface of the first portion and the side surface of the third portionto a center of the third depression is shorter than a length of thethird depression along the direction that the third portion extends. 17.The waveguide device of claim 1, further comprising another electricalconductor including another electrically conductive surface opposed tothe electrically conductive surface of the electrical conductor; whereinthe artificial magnetic conductor includes a plurality of electricallyconductive rods each including a leading end opposing the electricallyconductive surface and a root connected to the other electricallyconductive surface.
 18. The waveguide device of claim 1, furthercomprising another electrical conductor including another electricallyconductive surface opposed to the electrically conductive surface of theelectrical conductor; wherein the artificial magnetic conductor includesa plurality of electrically conductive rods each including a leading endopposing the electrically conductive surface and a root connected to theother electrically conductive surface; the at least two branches includeno more than two branches; and as seen through in a directionperpendicular or substantially perpendicular to the electricallyconductive surface, an outer edge of the enlarged gap portion reaches anedge of the two branches or the junction on an opposite side from thefirst portion.
 19. The waveguide device of claim 1, further comprisingan impedance transformer provided on at least one of the waveguidesurface of the first portion and the electrically conductive surfaceopposed to the waveguide surface of the first portion; wherein theimpedance transformer allows a capacitance between the waveguide surfaceand the electrically conductive surface to be increased from acapacitance at any adjacent site; and a length of the impedancetransformer as measured from the one end of the first portion along theone direction is equal to or greater than a width of the waveguidesurface.
 20. The waveguide device of claim 1, further comprising animpedance transformer provided on at least one of the waveguide surfaceof the first portion and the electrically conductive surface opposed tothe waveguide surface of the first portion; wherein the impedancetransformer allows a capacitance between the waveguide surface and theelectrically conductive surface to be increased from a capacitance atany adjacent site; a length of the impedance transformer as measuredfrom the one end of the first portion along the one direction is equalto or greater than a width of the waveguide surface; and the impedancetransformer makes a distance between the waveguide surface and theelectrically conductive surface smaller than at any adjacent site, ormakes a width of the waveguide surface greater than at any adjacentsite.
 21. An antenna device comprising: the waveguide device of claim17; and at least one antenna element that is connected to the waveguidedevice.
 22. An antenna device comprising: the waveguide device of claim18; and at least one antenna element that is connected to the waveguidedevice.
 23. A radar system comprising: the antenna device of claim 21;either one or both of a transmitter and a receiver connected to the slotantenna device; either one or both of an A/D converter connected to thereceiver and a D/A converter connected to the transmitter; and a signalprocessing circuit connected to the either one or both of the A/Dconverter and the D/A converter; wherein the either one or both of atransmitter and a receiver is implemented as a millimeter waveintegrated circuit; and the signal processing circuit performs at leastone of direction-of-arrival estimation and estimation of distance.
 24. Aradar system comprising: the antenna device of claim 22; either one orboth of a transmitter and a receiver connected to the slot antennadevice; either one or both of an A/D converter connected to the receiverand a D/A converter connected to the transmitter; and a signalprocessing circuit connected to the either one or both of the A/Dconverter and the D/A converter; wherein the either one or both of atransmitter and a receiver is implemented as a millimeter waveintegrated circuit; and the signal processing circuit performs at leastone of direction-of-arrival estimation and estimation of distance.
 25. Acommunication system comprising: the slot antenna device of claim 21;either one or both of a transmitter and a receiver connected to the slotantenna device; either one or both of an A/D converter connected to thereceiver and a D/A converter connected to the transmitter; and a signalprocessing circuit connected to the either one or both of the A/Dconverter and the D/A converter; wherein the signal processing circuitperforms at least one of encoding a digital signal and decoding adigital signal.
 26. A communication system comprising: the slot antennadevice of claim 22; either one or both of a transmitter and a receiverconnected to the slot antenna device; either one or both of an A/Dconverter connected to the receiver and a D/A converter connected to thetransmitter; and a signal processing circuit connected to the either oneor both of the A/D converter and the D/A converter; wherein the signalprocessing circuit performs at least one of encoding a digital signaland decoding a digital signal.